There's a wide range of paint programs under the $100 mark. As well as what's been mentioned already, I'd add;

Free; Deep Paint 2 (ex-commercial program) at

www.download.com/Deep-Paint/3000-2191_4-10398243.html

Reasonable cost; Corel Photopaint as part of the Corel Draw Suite. The current version is X3, and that's expensive, but legitimate (sometimes unused) earlier versions frequently appear on Ebay, say versions 11 or 12 for $70-80. I got a copy of version 9 for £10GB a couple of years ago, and it's still my main paint program.