You can also look on Ebay. These are real, not pirated, software packages. Most important is to make sure that they can be upgraded. Sometimes their are limitations on the student versions.
Something that might save you a little is that version 5.5 just came out and you may want to see if any 5.0 versions are available at a lower price. You can see the upgrade details
here . It all depends on what you want to do.