They idea is nice but, i am afraid that as most of this articles the title is a little misleading... you had a sale but not yet delivered a product, that is wha

They idea is nice but, i am afraid that as most of this articles the title is a little misleading... you had a sale but not yet delivered a product, that is what the customer paid for. So you still have to work and even with all the limits you pose this might take 3/4 hours... and supposing you work at an hourly rate of 20$/h witch i think(but i'm not sure) it's quite low you might "spend" 60/80 $ of your time to develop it. this gives you a profit of 10/30 $ depending on how fast you are. Anyway this is a nice project and i really hope you or someone else will prove my calculations wrong! Good luck ;)