I know someone who sells pony plushes for 20 dollars on ebay. Everyone else is ripping you off.
It depends on the cost of the materials used, the size of the plush, the quality of the stitching, the overall quality of the plush, how the eyes and cutie mark were made, -and- whether or not they made their own pattern. Plus if it took several hours of work rather than just a couple, that goes into the pricing as well.
There's a ton of factors that go into pricing these things. Most of the 50$+ plushies I've seen are well worth it. Anything lower than 50$ on a plush like this or this the seller would be working for free and not making much of a profit. They'd be ripping -themselves- off.
You're not paying for some little inaccurate plush made by a combination of machines and some little Asian children- you're paying for something that one person put their time and talent into to assure accuracy, durability, and quality.
The person I'm talking about made it look like the ones people are charging 200 for and some people charging 200 dollars they look like the link you showed me. I wish I remembered her dA but she made it on dA's front page with Rainbow dash she sold for 20 dollars.