As much as they're willing to pay I guess. If they give you 30 grand, you can use some pretty damn good clay.
I guess the money is more about getting it into an exhibit so liberals can eat wine and cheese while pontificating about what it means so they feel intellectual.
Ah yes, sniveling art history professors wearing tweed jackets with suede on the elbows, wire rimmed glasses, sporting a beard. "Yes, mmm yes, I see what he's going for here. Yes, very interesting. The clay symbolizes the layers of facade society places upon us and the BLAH BLAH BLAH *VOMIT* FART NOM NOM NOM......... Yes, did I mention I'm going on sabatical in two months, anyway, what a wonderful Cabernet Sauvignon...... Oyster Bay?"
I despise these people.