So here are some alternatives that will cost you nothing, nada, zip, zero, zilch, goose egg:
1. Gimp. "GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring." Here is an introduction page, and here is a tutorial page so you can take a look at what it can do.
2. Fotografix. "While graphic design professionals probably wouldn't be able to substitute Fotografix for Photoshop, it's certainly a capable free alternative for the average Joe."
3. Paint.NET. "Paint.NET is free image and photo editing software for computers that run Windows." You will find the features list here, and tutorials here.
4. Photoscape. "Photoscape is the fun and easy photo editing software that enables you to fix and enhance photos." You can take a look at some screenshots here.
5. Adobe Photoshop Online. The title pretty much says it all, and you can take a test drive here.
If you know of any no cost Photoshop alternatives that I have not listed here, please let me know and I will be sure to post them.