Realistically, how much actual, out of pocket expense in paper and chemicals will you be incurring to make 3 8x10 prints? Obviously you will have some time invested in making the prints as well, but if you already have a finished 11x14 print and you kept good notes, making 8x10's should not be that time consuming, at least for one of the prints. And consider that whenever a photographer makes prints for sale at a gallery, those are on "spec" as well, with no guarantee that they will ever sell.

If it were me, I would make the prints and deliver them to the client along with an invoice. I would tell them that if they had specific, objective issues with the prints after inspecting them, that they could return the prints to me at no cost. When you make art you put a lot out there (your time, materials, self-worth) with absolutely no assurance that reward will follow.