If it's something I love and would consider paying full price at a LQS, I'd probably go up to $5 a yard. Anything else, I'm looking for a screaming deal. It's got to be priced better than a sale price at a fabric store, because at the fabric store I can buy what I want, as much as I want, and know it's unwashed and brand new.
I think selling quilt fabric would be a painful experience if one were always thinking about how much one paid for the fabric in the first place...