you know, it all comes down to how picky you are. bought a previous addition for last physiology class for 5 dollars shipped (used of course). Yeah, i didn't have few new pages and an updated intro, and it was highighted...but who cares??? you can easily get a loan copy in the library and photocopy the pages. saved myself 70 dollars.
are you a bio major? if you plan on going to grad school, MS/PhD/Professional school, you WILL end up using those books again. I just finished up my MS in Physio, I did not buy a single book, however, I did go back to my old physiology books for reference, ALOT.
Typically, I have one book for each subject, chem/bio/physio/neuro/micro/immunology and maybe a biochem book, bought all this in undergrad, info here should be sufficient to get you through most classes. If you need something clarified you can always google/wiki/ask your prof. New data normally comes from journal and review articles which you can download for free through your library services.