You could - at least - put up a sign that says
"Of course you can make it - but when?"
The only thing I am willing to buy at craft fairs are those crocheted, nylon, pot scrubbers.
There have been a couple of things I would have been willing to pay for the instructions/pattern - the 9 x 13 casserole carrier, for one thing.
You could also put up signs saying - if you want to make it yourself, this is what it would cost - with a material and cost sheet posted.
So - sorry - I really don't have any helpful ideas.
But good luck with whatever you do.