Cheapest Animal items are usually in the shops (and not all shops have animal items!)
So I'll be posting a list of shops here. There are 3 buttons at the top of each shop, (human + animal), (human only), and (animal only). Click animal only to view - most shops only have ONE page of animal items.
Loyal's Bazaar
Loyal's Bazaar Not to be missed if you have access, most expensive item is the Angelic Quartz Halo @ 500,000,000 gold. IMHO: Hair extensions and OMG/AFK hats, several recolours of Angelic Minis/Nitemare Minis. CUTE CHEAP ANIMAL COURIER BAGS at 28,800 gold each, what's not to love about Loyal's? XD HELP: If you can't get into Loyal's yet, here is a thread selling LB items at store price if I'm not on. (I'm a helper in the thread and you can PM me a list). FULL LIST of LB items. (updated as of 07JUL2014)
Barton Boutique
Barton Boutique Most expensive item are the Basic (colour) Dress at 1980 gold each. They're rather hard to match and look rather ... unpolished. (likewise the Basic Jacket , Shorts , and Skirts - the T-shirts and Jeans are more useful when combining with other items as an UNDER layer) IMHO: The most versatile items here are the Basic (color) hats ( 1320 gold each), socks (socks 540 gold, stockings 600 gold) and shoes (Mary Janes 540 gold, Sneakers 480 gold). The hairpins (480 gold) and hairbows (600 gold) makes a lovely accent on the Basic hats!
The Jockstrap
The Jockstrap Most expensive items here are the Raincoats @ 2100 gold each. Not very versatile, but is probably the cheapest hoodie animal item available. Two poses, hood up and down. IMHO: Best bang for your gold here are probably the Bucket Hats ( 1320 gold, great for formal wear) and Rain boots ( 900 gold, when you need bigger feet than Mary Janes or Sneakers XD) Skip the scarves, they're rather bulky and hard to match again.
Ruby's Rack
Ruby's Rack Most expensive item is 3600 gold, the Madeline hats (straw hats with ribbon. Add a Paw Clip or flowers/hairpins from Buttercup Cafe or hairpins from Barton Boutique for accents!) IMHO: The picnic blankets (1800) gold are probably the cheapest animal background mod items, mind, the layering doesn't work with a lot of TAIL items (such as Golden Glow or Myotan/Myatama).
Crosstitch
Crosstitch Fancy duds, most expensive at 30,000 gold! IMHO: Pair the Dapper Scamp ( 30,000 gold) with the Bucket Hats from The Jockstrap for a mafia look. Add Jeans from Barton Boutiquewith the Winter Punk Coats (30,000 gold). Think the Cutie Love Armour (30,000 gold) is hard to work with? Try the Myotan/Myatama dresses for a bit of a flare, or if strapped for cash, Barton Boutique for Jeans and skirts, or Ruby's Rack for Bloomers XD. My favourite items here are the Blossoming Bao (20,000 gold), a must for any girly animal who aims to be sugar and spice and everything nice!
Barton Jewellers
Barton Jewellers Just 660 gold for glasses, two styles and four colours each! (gold/silver/black/brown). IMHO: unless you have a REALLY BIG eye mod, stick with the basic round glasses instead of the basic square , as it obscures the eyes. The one I use the most often is the Basic Black Round Glasses.
Salon Durem
Salon Durem Give your inner animal a whole new 'do! There's only THREE prices - Cheapest is NO HAIR (100g), midrange Ruffles @ 9,600 gold + 24 colours, most expensive are 10,500 gold ( Creampuff style, Bookish style, and Pompadour Style, All 24 colours each ). This is a very heavily subjective your own taste thing - should be pretty easy to browse since there's only 2 pages worth of hair.
Skintyte
Skintyte Get a new skin for just 150,000 gold! More expensive furs are purchased only with Gaia cash, most expensive being Panda Fur @ 3500 Gaiacash. IMHO: The WORST 150k skin I've worked with are the pale green. You might be more creative than I am, so good luck to you if you are, since those are usually in vend for 100k gold. If you can't afford a skin, buy a muzzle (4500 gold) and eyebrows (2500 gold, various moods) to liven up your expresson.
Buttercup Cafe
Buttercup Cafe MOST EXPENSIVE ITEM ONLY 6420 gold, do not buy overpriced vend items! IMHO: gawd too many to list and all so cute! Food for your hands and mouth, and flowers for your chest/dresses and hairpins for your head! There's at least ONE that'll add extra sparkle to your animal Outfit.
ANY SHOP NOT CURRENTLY LISTED = NO ANIMAL ITEMS
Next post will be cheap animal non-shop items/freebie grants.
Golden Glow and Flare Forever. Good when you want to cosplay a flame tailed Firelizard. it's also VERY useful in changing skin color (con: removes the tails/ears on all animal bases and makes it impossible to add eyebrow layering, but can still do muzzle mods. Eyebrows/Muzzles can be found in Skintyte). Poses: Hair, flaming tail, eyes, fanged mouth, Lizard Skin, vest, baggy shorts, and shoes. The fanged mouth can ALSO be useful in doing a Deidrich cosplay what with the free green bunny skin grant last Kickstarter. Flare Forever has AI'ed to 150 mil, but you can still pick up Golden Glow at UNDER 10 mil when it's listed. I got my last one for 7 mil yesterday. The THIRD recolor Blaze Eternal is currently 2 bil.
Ivy's Adjustability and Vienna's Adaptability are two color variations of the same VERSATILE multipose item, comes with headpiece, hair, eyes, bushy fox tail, capelet, and dress. They are both usually around 30 mil, but Ivy's has AI'ed to 75 mil with Vienna's close behind at 40 mil.
Mysterious Myotan and Miraculous Myatama, again two color variations of the same VERSATILE multipose item, comes with hair, headbow, eyes, arm and leg mod poses, top, skirt, and long poofy curling kitty tail (the hair itself is also shaped like kitty ears for added accentuation to skin mods!). CHEAPEST animal leg/arm mod, suitable for most girly sweet animal avs, around 60,000,000 gold on average. The third recolor option, Magical Myuchama is 12 bil.
Ribbon Candy, the animal version of Ribbon Candy (human), with identical poses of : head ribbon, hair, eyes, poofy sleeves, dress, and lacey shoes. 500 mil CHEAPER than its human version at 100 mil, sometimes there are listings of 70 mil.
LESS versatile multipose non-shop s**t (aka I had trouble putting together outfits with them but you may be more creative)
Magical Blue Paws (~55 mil) and Magical Yellow Paws (~40mil, NO LISTINGS atm) are the CHEAPEST animal versions of the Magical Girl's (Colour) Uniform. I found it of limited use except for the bow as chest decoration, if not in a full set of four. (or at least two, with the Myotan/Myatama leg/arm mods instead) Magical Paws also come in Red, Purple, Black, Pink, and Green.
Junior Professor, the animal version ofJunior Professor (human). Identical poses of cap, colored hair bangs, sweater, bottom (it looks like it has shoes but doesn't, need socks/shoes if you have avatar sitting down), shoulder bag. USUALLY around 40 mil, AI'ed to 80 mil. It's INSANELY HARD TO PAIR with current animal store outfit colours, you need at least two, sweater+pants or sweater+shoulderbag/cap options if you like going pantsless on animal avatars.
Matsuri Specialties, ~ 30,000,000 gold. Each with Four Diff handheld Poses: Sparkler, Cotton Candy, Water Balloon, Shaved Ice, BBQ Squid on a stick. Some of the arm poses are rather awkward, if you just want a FOOD item for your critter, you're probably better off in Buttercup Cafe where the most expensive food is only 6420 gold. The Sparkler is, however, useful for magical girl/firelizard accents.
Sukumizu, ~75 mil. Four poses: Goggles, neck ribbon (HARD to pair, I've tried with ALL the store basic dresses and all the dress poses in this post), swimsuit (look like a middleschooler from japan in swimwear!), and watergun. The most useful is the goggles for more masculine animal avatars (like Flare Forever/Golden Glow/Junior Professor).
North Star Penguin. Used to be 30 mil, AI'ed to 100 mil. 7 Poses: Penguin Plushie, Penguin Plushie (sit), Penguin hoodie, Penguin suit, Penguin shoes, Orange Scarf, Stars trailing on top your head. The most useful poses are the Scarf and the Stars on top - great accent for ANY outfit.
Pretty Teaset is the CHEAPEST of the Teaset colours for your Teacup puppy/kitty cosplay. Used to be 70 mil-ish, AI'ed to 135 mil, same as the Gothic Teaset (no listings ATM). 5 Poses: In the Teacup, Teacup on your head, handheld teacup, Tea-stained sleeveless vest, and teabag necktie. It's easier to colour match the Gothic Teaset vest than the Pretty Teaset vest. The most useful is INSIDE the Teacup + handheld poses, but for the latter you might as well go to Buttercup Cafe and buy yourself a proper spot of tea for under 1,000 gold.
Wish Granter, 130,000,000 gold. Make your animal a genie! 5 Poses: Genie Face, Jewellery (hard to see tho), Hair (top knot), Arm mod (crossed arm pose w/ bolero), and bottom (legless blue wisp coming out of a lamp)
North Kitten Star, usually 100 mil, AI'ed to 300 mil. 7 Poses: Sit, (>w<) face, ankle nuzzling, leaping attack, handheld (right or left arm, but the left arm pose looks HORRIBLE and obscures the face), On the head (does NOT work with most hair/head/skin mods!), and I Am North Kitten Star (IMHO the only reason for this pose is to give you a CHEAPER alternative to the same pose for North Kitten Star {human, AI'ed to 5 bil} ).
Skipping the Kickstarter grant skins because I HATE THEM ALL. The colours are INSANE to match (the current Hidden tome, Nocturnal fawn is hard to see and almost solid black, Sunrise looks like a PIG, the previous Loyal's/Beach party Deidrich & Prunny are too BRIGHT Green and Purple respectively).
Reply
@ 500,000,000 gold.
at 28,800 gold each, what's not to love about Loyal's? XD
at 1980 gold each.
, Shorts 
, and Skirts 
- the T-shirts 
and Jeans 
are more useful when combining with other items as an UNDER layer)
1320 gold each), socks (socks 540 gold, stockings 600 gold) and shoes (Mary Janes 540 gold, Sneakers 480 gold).
1320 gold, great for formal wear) and Rain boots (
900 gold, when you need bigger feet than Mary Janes or Sneakers XD)
30,000 gold) with the Bucket Hats from 
30,000 gold).
30,000 gold) is hard to work with? Try the Myotan/Myatama dresses for a bit of a flare, or if strapped for cash, 
20,000 gold), a must for any girly animal who aims to be sugar and spice and everything nice!
, as it obscures the eyes.
(100g), midrange Ruffles 
@ 9,600 gold + 24 colours, most expensive are 10,500 gold (
Creampuff style, 
Bookish style, and 
Pompadour Style, All 24 colours each ).
Panda Fur @ 3500 Gaiacash. 
4500 gold) and eyebrows (2500 gold, various moods) to liven up your expresson.
Golden Glow
Flare Forever.
Blaze Eternal
Ivy's Adjustability
Vienna's Adaptability
Mysterious Myotan
Miraculous Myatama
Magical Myuchama
Ribbon Candy
Ribbon Candy (human)
Magical Blue Paws
Magical Yellow Paws
Junior Professor
Junior Professor (human)
Sukumizu
North Star Penguin
Pretty Teaset
Gothic Teaset 
Wish Granter
North Kitten Star
Ringa Ling
Paw Clip
Earth Day Leaf Hat. 
Nom Nom.
2k14 Betty's Bow
Jiggly Eyes