Don't you sell photographs (monthly, bi-monthly specials?) on your website for around $400.00(?) that are 1/2 the going gallery rate? If that's the case then 1/2 that price, or $200.00, would seem about right for this project. No offence, but $400.00 for a reproduction is crazy.
I would refuse to sign them the same way as my original photographs, have it clearly stated on the back how they were produced, and would have my website printed on the back as well.
They want you...make them work for it and squeeze as much out of them as you can...
I can't wait to post a dilemma like this