I've never priced any such things, but in general, people can (& often do) charge whatever they figure they can get away with. There's time, effort & costs involved to raise any sort of creature, & no one's forcing you to buy from them. You could try running a (free?) 'want ad' for a wolf spider- see if anyone has one they want to get out of their house. But how many people know a wolf spider when they see one? But someone might- you could offer a price for a healthy one- try $10 or $15? And you could put a pic or link to a pic of one in your ad, to be sure they know what you're wanting.