Gorgeboy, welcome to the Guild!
By your price limitations, I'd say go GIMP as its free. Photoshop is something like $800, maybe less, haven't checked lately. I use Xara Xtreme Pro 4.0, but Xara offers a perfectly adequete version at $70 to make all the maps I do. I use the pro version, as I do other kinds of graphic design using the more expensive application.
Also, if I'm not mistaken Campaign Cartographer 3 is only $40 - if you get all the supplemental software: Dungeon Design, City Designer, Cosmographer, etc, you're talkin' more money, perhaps $300 (though I wasn't aware of that.)
If you go the free route with GIMP, also consider Inkscape which is a vector drawing application - great for labeling, river creating and other features on top of a map generated in GIMP. Like GIMP, Inkscape is free - though both have learning curves.
Good luck on whichever way you decide!
And again, welcome!