Some advice. I could be wrong here but I think it might be good advice.
Work out how much it costs you to make the cap including time, and base your asking price on that + how much caps usually sell for.
People like to be given a price, if they aren't they may not bother when otherwise they would. I know it's difficult to set a price when starting out but you will get more sales if you do I think, provided you chose a good price. You can always adjust it.