well, maybe you could reasearch what the going rate is for novel cover photography/art. and then choose a middle ground between the highest and lowest rate. it would be fair because you haven't been on a national bestseller as of yet, but it wouldn't be as if you are discrediting your talent.

I would just ask for a small percentage of book sales. However much that would be, and it seems fair. Plus, ask for credit, definatly.

Definitely get credit, and charge them what you think they'll accept for an easy deal, really

Hell yes!

Absolutely. You drew it, you deserve the credit. Especially if he makes profit.

Yeah, they should pay for it if their using it! Or at least get them to give you credit, as *Josh-Tequila said.

Yes or at least get credit for it.