Wenger makes a good cheap laptop bag.
http://www.amazon.com/Swiss-Gear-Ibe...p_ob_e_title_1 I use the 15" version of this. If you can wait for sales, you can find this for $30. Keep an eye out on slickdeals towards the ends of the semester (next few months).
If your campus is anything like mine was, get a proper backpack, not a messenger bag style. I tried the messenger bag style for a while, but with my books, notebooks, laptop, etc, it killed my shoulders. Do yourself a favor and go with the good old backpack.