Others will chime in also but this is what I would do.
Consider the pattern (block), how long did it take to sew it? Did you buy the fabric? How would you want to be compensated for your time? Add it all up and maybe pad the amount or tone it down depending on whom you're sewing it for. :-D :-D
Did a search on QB:
http://www.quiltingboard.com/t-8711-1.htm