Can you describe a small game you'd make for 20$? Also, you should answer the question about asset making (do you have to make them, or are they provided). I'm not trying to steal your work or anything, but we can tell you more solid things if we can get a grasp about how complex these game would be.
Personally for 20$, I'd make a very simple game with minimal logic. And they could forget the .capx for that price. Just as tunepunk said, that's an insult. People who don't understand how software development works can easily offer way less money than they should. These people expect everything to come cheap and easy. I've had my fair share with customers like yours and my advices are:
- Expect a lot more work than you'd think now.
- Expect a lot of problems with the game.
- Expect that the customer will complain.
Unfortunately it's never as easy as just making the game (or app or website, etc.) and being done with it.