that's a more than fair price. The author or someone is going to want to negotiate rights. They'll want full use for that price.
Be warned if you don't give them that - they may go elsewhere.
But you could triple that price for full rights and say that the price you gave is for first publishing rights only and ask for % royalties on other printings... that may make you more in the long run and is how you could work towards retirement.
also are these full color and what's the style of the book? I too would talk to the writer and make sure you get some royalties out of this and CREDIT. you want people to know it is your work cause it could lead to more in the future. hopefully the publisher likes your work, even if they don't like the story you might get some gigs out of this regardless. Good luck and keep us informed.
'I will become the most powerful Jedi ever!'
'I'm the damn designer, bitches!'
I charge $150 per page and what they do with it is what they do. That is just me, I don't go by a standard, I usually request a copy of the book after publication for free or more, christmas gifts. I am sure there are others that charge more, but I usually gain a relationship with the person and that seems like a fair price for me. To me it's alot about relations and what will I gain from the experience.
I think coconut has good advice. You also might go to www.lisavictoria.net and ask her...she's the illustrator for Triplex Coniunctio which is a fantasy fiction book by my sister that just came out last week. I do her book covers and her web/print work and I did the 1st cover pro bono (hey...she's my sister!) but its now written into the contract w/ the publisher that I get $400 per cover. Coconut makes a good point that a lot can bear on relationship with the author. Doing illustration work for printed books becomes a potentially great way to make new clients through referrals and publishers. Good luck! Would love to see some of your work!
Knowledge speaks but wisdom listens....Jimi Hendrix