While older students may sell you older editions .. they often sell them far cheaper than the used copies at titles/bookstore. I think most of the books i saw going used were in the like 20-40 dollar range for textbooks that go for $200+ new.
Talk to the prof. See what editions they are ok with. Get the cheapest you can. The campus bookstore should always be your absolute, absolute last resort. Its pretty easy to spend either $100 (if you are smart) or $2000 (if you buy new) for first year textbooks.
Other ideas to save money are
-International editions from Amazon or (even better)
http://www.abebooks.com/
-Pirate. If a prof says you NEED the new edition that just came out then they are probably an a**hole who signed a contract with the publisher to get a cut of the profits. When looking for pirated books the piratebay is pretty good. If that fails then
1) Use adblock when searching (helps to prevent viruses)
2) Use Bing because google is really good at throwing any useful pirated stuff to like page 30 in search results
3) Search with filetype. Ex. "my book title" -filetype:pdf
4) ^That works almost every time. If not talk to upper years and fellow class mates to see what resources are floating around.
