Good starter is Photoshop Elements, its like light versio of "real" Photoshop, Elements cant do all tricks but i was pleased with it when i tried that (2.0 came with my camera), i think current is Elements 4.0 and costs way below $100 i think.
If you want full Photoshop, you only need that part of it, there is full Creativity Suite packages that do cost arm and leg ($1500 or more) and has nearly all Adobe products, i do have Photoshop CS2 right now... and comes with 2 extra softwares like Bridge that is picture manager etc and ImageReady that allows you to make animated gifs for example... sure even that costs like... $700. prices really do vary alot, in here that Photoshop CS2 can have $400 price difference
so doing research is good.
hope that helped