Ask the event organizers. They may welcome such an item, and will be happy to have you make them. You might even offer to make a given number, which they could buy for a reasonable price, and mark them up to sell themselves. That way you don't get stuck with unsold items.
One way to make cash sales easier is to round up the price to a dollar amount and take the taxes of on the back end, ie. after you get home. That way you don't need any loose change. And you could price in $5,00 amounts and you would use fewer ones.
Unless you're Canadian, where you use coins for ones.
In your situation, I would find private studio space. Unless you want to try to patent your process, you can't really stop someone else from trying to replicate it.
That said, whatever work another person does with your process will stil be different from your work.
Imagine if the inventor of the potters wheel had said "I spent years making this thing work! No-one else can make pottery using this technique!". Or if there was a copyright fight over calculus.
In papermaking, there are different additives you put in your pulp to help it bind together. You use different ones depending on the type of fiber you're using. If you mix them together, you get some neat effects. I did this by mistake. Later I learned that someone tried to patent mixing those two additives together, as a unique process.
Personally, I like to share stuff. I share recipes and ideas all the time. Maybe someone else will do niftier things with my idea than I could.
I can't seem to figure out how to import a picture from Facebook, but if you check out Dark River pottery there you can see our set up for several size shows, from 2 six foot tables to three sides of a 10x10 space.