Getting CC0 game art for ~15€?

Getting CC0 game art for ~15€?

Today I got caught totally off guard as I was gifted the game Aquaria from icculus. The story: I offered 15€ worth of BTC but was humbly asked to keep them. "Thanks, but keep the Bitcoin. :)". This I interpret meaning that my enthusiasm counts much more than my money.

As I was given this gift I would also like to give a gift by letting somebody create or build upon/improve some CC0 art that has been contributed(or can be contributed) to the Flare RPG game.

Last time I 'contracted' Dread Knight for Flare Buckler Improved for 1BTC(~15 - ~16 USD). Maybe I gave too much but still I'm happy, though this time I wanna be more sure of what something may be worth so I can feel, and the artist can feel, this art is worth it.

What I need help with is if you have any ideas of what could be worth ~15€ of open game art in Flare RPG? Maybe it is hard to tell because going strictly for CC0 art may limit the work one can do.