Good idea, looks like good execution, not a bad price at all. Good work, particularly if it's paying for itself!
If I were going to add anything, it would be that you look into an electric version. Cox engines sometimes take a lot of flogging to run, fuel smells, it's noisy, you have to _find_ high nitro fuel, etc., etc.
If you could stand the thought of sourcing the electrics from Taiwan, and you could hit a price point that was even $10 or $20 higher, a "flick the switch and fly" airplane may have some appeal -- and kids would be a lot less likely to get run off of an urban playground for flying an electric.