It's a commodity market. If the prices are too high, someone can list lower. You even have in game market and limit orders. Something is worth what something is.

Sataria is very scarce. Mending is particularly hard to find and only really able to get by fishing. It's an easy 10-20K sats and that's with very few players. Many items on our SMP server are nearly free and so people can pay another player who has mined very little if they simply want to build.