[thejeff]

Cheap Tarts are actually balanced better. That lets those who don't have the Chalice and/or GoH summon enough to get useful ones.
If they were sufficiently expensive then they'd only be worthwhile if you could cure all you got and whoever could hold onto the Chalice/GoH would dominate.

If you could change mechanics to balance them better, I'd make them uncurable, even by the Chalice/GoH.