I know that it sounds like an oxymoron to use "cheap" and "Adobe" in the same sentence, but don't forget about the student discounts available. Go to a site like
Academic Software, Student Discounts : Gradware : Educational Software Savings and you'll see Adobe products at much more reasonable prices than anywhere else. All you have to do is send in proof that you're a student. If you're not a student, you might have a student in your household. Or in your neighborhood. For example, whether he knows it or not, my 13-year-old son is about to purchase Lightroom 2 for only US$100. All I have to do is get a statement from his school verifying that he's enrolled.
I've never used Gimp, but I really trust Adobe. I use several of their products every day in my work, and I have nothing but praise for them. Plus, as someone has already mentioned here, Adobe products are the standard for photography. When I scan through all the photography magazines at Barnes & Noble, almost all of them have tips and tricks for Adobe products. And with the low prices available on education-discount sites, I'm going to stick with the standard.
Good luck,
Pappy