If you are looking for a good, inexpensive image editor, Acorn 4 for Mac is on sale for a limited time for $14.99. I bought it through the App Store and was able to install it on both my computers (bonus!). If you prefer, you can buy it directly from the Flying Meat website.
Acorn is a good-quality, Photoshop-like program, without the Photoshop price. I use it all the time to create graphics for FileMaker elements. I think I first heard about it at DevCon a couple of years ago from Matt Petrowsky of FileMaker Magazine. The regular price is $49.99, which even then is still pretty reasonable.
I don’t know how long it will be on sale, so check it out!