For those prices, its a little OP, and takes the challenge away a little bit, which in this case would become a bad thing. When you go out into the wilderness and find these mobs or get them from a friend it makes it more difficult, therefore the wealth you receive from it is word rewarding. This isn't actually that bad of a proposal though, because where some people live there are no mobs around a reasonable distance, and you cant sell animal produces besides whool at the shop for money.
