Adobe Photoshop is overpriced, but there is no competition.
I really hate adobe. Adobe reader that pile of shit program is on almost everyone's fucking computer. One of my many pet peeves when I fix friend and family's computers.
Anyway, adobe's editing software is powerful, professional and well coded. That said it is still overpriced (but it can be when big businesses use it).
I'd try to do what Gekko suggested and get a student copy or something. Or i'd just head on over to the pirate bay....
