We looked at buying a gas fired Lil Orbits machine about a year ago. May still consider it if we can find some cold weather events to attend. Hot Cider  Hot Chocolate  Hot Donuts would sell well at Holiday festivals.
The machines are automated, mix the batter, pour it in the machine and removed the cooked donuts. The main thing to look for is what can of power you need to operate the machine.  The small machine can either ordered to run off 120v or 220v. The larger machine runs off of 220v. So depending on where you plan to set up make sure you have the power you need. Most of the machines came with a kit that included the mixer, pourer, and supplies.
Check out http://www.minidonuts.com[/font%5D%5B/size%5D
A word or warning. When we were looking into buying a machine there was a scam going around on Ebay offering cheap machines. Several people sent in the payment but never received a machine. If you can t touch it don t buy it unless it is form a reliable dealer.