By what you have said I still don't think he's gotten the point. So may I suggest you make a date with him to go to the fabric store to buy the materials that are needed to make one quilt. Doesn't matter what size because this is just a lesson. Now you don't have to really buy the fabric but give him a list of what is needed to make your quilt. Have some sort of pattern in mind so this will help him with picking the fabrics out as well as be sure to have enough of each one. Take him on his tour and he is to right down the cost of each fabric and do the math so he knows how much each piece cost. Now don't forget the thread, batting, binding, backing and anything else used to make the quilt. Now ask him if he's willing to spend his money and time to make this quilt and sell it for $50.
I think he will better understand what he is asking you to do. And that's still not including the time to make it.
I did this with my daughter a few years ago because she had no idea either. It worked better then talking with her about it. She will ask if I will make a quilt for her but is now more willing to pay for the materials. I'm still mom so I never charge her for labor, I just tell her I'm taking it out of her inheritance by treating myself to a day shopping at the fabric store. LOL