I'm lucky, as I can get PS CS4 for academic pricing, about $240
However, my brother runs PS Elements on his laptop and I've used it a couple of times. I don't know how good it'd be for the type of processing we do, as many of the functions that you'd normally expect in PS are automated and some have been combined to do a raft of jobs simultaneously. I suppose you could give it a try, though. Two other good programs to use are PaintShop Pro and The GIMP. PSP will set you back about $200, The GIMP is free. They're both very powerful programs and can do pretty much all of what you can do with PS.
I do most of my processing on my Mac with The GIMP, but I'm thinking of getting CS4 as well. Use them a complimentary programs.