you can usually get them from reserve for a few hours - and if you borrow them last thing before the library closes, you get to keep them for the night.
I found with the really expensive ones, a few hours a week in the library and photocopies of the pictures / summaries (like for anatomy) was enough - saved me hundreds!
Second hand is fine for most things, especially things that don't change much from year to year - but remember that the page refs for readings will be warped, so you might have to borrow the current book to translate the reading page numbers etc.