Expensive ones have a higher chance of netting you better gear, but I think the less expensive ones offer you a slightly better chance of getting better scrolls. So, that depends what you're doing it for, the scrolls or the gear. Scrolls are temporary, but can be used by anyone, gear eats up power, but is permanent. I have a LOT of stuff I can't use yet.
Right now, I'm trying to puzzle out Action Sets or what have you, since Luthorne, my High Assassin, just hit 25. I probably screwed up my build, but meh. Also, what the fuck is 'precision'? Do they mean perception, or is it something completely different?