The only assumption I'm making is that the card will have been tested and balanced.
I don't see any fundamental problem with a $1 card - it would force rethinking certain upgrade paths but most new expansions force rethinking how older cards work.
Fundamentally, the key to this set would seem to hinge on how cards that care about the Trash are handled. Removing cards from the trash, checking the contents of the trash, and checking the number of cards in the trash are all different concepts.
Consider Example: Dumpster Diver ($X) - Action -
Under the first: Gain a Trashed Card
Under the second: Gain a Copy of a Trashed Card
Under the third: You May Gain a Card Costing $1 for every 3 Trashed Cards
With the first the card is no longer in the trash (and unavailable for anybody else). With the second the card remains trashed but a copy is removed from the supply. In the third case the card becomes more powerful as the number of cards in the trash grows.
In any case, the expansion is going to make us pay attention to the trash. Something is going to get reconsidered, probably trash for benefit cards (e.g. Bishop), mass trashers (e.g. Chapel), or upgraders (e.g. Remake). More importantly, expansion sets tend to have cards that work well together. The same-set combos of trash / upgrade seem quite interesting.