$20 seems a bit steep though with no full support, clean or fully commented code but hey it's down to you. It's not something im personally interested in but good luck selling it.
I should hire you to do some coding for me sometime if you think $20 is steep for this much work. If you don't get it from Bill, you're going to do it yourself and you would have to value your time at practically nothing to think that was a good deal. If I look around for students and people or Eastern Europe, Far East, etc, I can maybe get an hour of work for that, whereas I might get 30 minutes anywhere else. I'd be very impressed by anyone who could write what Bill's written in less than half an hour.
This community never ceases to amuse me though. $20 on pizza and drinks? No problem. $20 for a movie and popcorn? Sure. $20 to save you several months of coding? That's a bit steep!