The first thing about lolita is that it's not going to be cheap, no matter what. Even if you buy things offbrand or second hand, theres so many components to making coords that you're still going to be looking at a decent amount of money, depending on where you buy things though you'll still be looking at around 100-300$ or more.
There's a lot of ways to go about it, buying brand or offbrand depends entirely on you and how much you like the style. I've heard a lot of people say that if you're interested in lolita, save up the money and invest in a dress that you really love but if you're also just looking to try it out then offbrand might be a better option !
There are a lot of places to find lolita clothes and the best places I've found are facebooks sales
[lovely list of them right here] where it's easy to access, it'll be a bit cheaper and most people speak english !
Most people who start lolita and are looking for a cheaper option, (because if you're not sure you'll like it then there's no point in spending 300$ on a dress right?) tend to look at Bodyline which has some nice things if you look hard enough and they also carry different styles if you're into, sweet, goth, classic, it's also a really great place to buy blouses but a terrible place to buy petticoats because they deflate really quickly.
I think lolita takes a lot of time to get into and you need to decide what style you think you'll like best, not saying you can't try them all, but really give it some thought instead of jumping head first and then realizing you're stuck with clothes you don't really like ^^
Sorry for the wall of text oh my goodness. This is entirely my opinion though but hope this helps though ~