If you're looking at an image editor at all like Photoshop. Try GIMP it's free to use Open Source software - it won't cost you anything at all. Learn to use it. There is a learning curve as with any software.

That said, I don't use either Photoshop or Campaign Cartographer. I prefer using a vector drawing application, Xara Designer Pro x11, but I use that software for a lot more things than just mapping.