Photoshop Elements is the budget version as far as I know. You can even get it free when you buy a wacom intuos tablet! (I opted for sketchbook though, so I've not actually used elements, but I read it has lots of the features that Photoshop has and I imagine it will suit most of your cartographic purposes.)

Otherwise, yes, if you plan on buying CS4 or whatever, you'll be paying lots of money.