What is the best carrying case for a college student with a 13" macbook pro?

I will be a freshman in college next year and need a case that will protect my laptop, fit a couple of binders or textbooks, and still not be too bulky. I prefer a bag that hangs with a single shoulder strap on my side (like a messenger bag). I would also really like to stay relatively inexpensive (less than $100). So, easy to carry, protective, with a little extra room, and relatively cheap. Any suggestions?