Never used either, and considering purchasing myself. From what I've read on the internet (so it must be true):

Lightroom runs faster
Lightroom runs on PCs and Macs
Aperture is Mac only.
Aperture has a "better" and less-modal UI.
Aperture has a loupe function that people seem to really like.
Many people seem to like how Aperture organizes and imports better.

Both have free 30-day trial versions, so it may be best to just try them out. As for price, I know that Lightroom has a student discount, and knowing Apple I bet that Aperture does too.