I made a three-sheet Excel workbook for pricing one product at a farmers market, bake sale, or popup. It takes the batch cost, the stall fee, and the card fee, then rounds to a sign price. The sample is a jam jar: cost about $5.38, sign price $13.50. Yellow cells are the ones you replace with your own numbers. It is $9 here:
https://stallprice.itch.io/stall-price
