Paint shop pro is better then gimp and paint.net. It costs about $100. If you get it with a coupon you could probably get it for 60 bucks. Its what I paid. And 20 more for the upgrade to the newest version that just came out.
Photoshop is $1000 unless you get it through an educational discount as a student which you need a university id and some other things for.
GIMP and PSP are free but they do not have all the polished goodies of PSP or PS.
Its up to you as to what you want to use. I use PSP Photo X2 Ultimate and PS CS3. I love both, i have found the pen tool easier to master in PSP. But again its about which one you learn first i suppose.