First off, every book you see is free. You only need to know how to take it. But if you are too skittish for that there are a number of other sources... Your local infoshop may have a lending library. Your friends might be willing to share their books with you. Public libraries tend to lack much but are also worth a try. You could see if you can enter the libraries of local colleges or universities as a "visiting [or independent] scholar" - many will grant you access, but they rarely have a free method of getting books loaned out.
If you would be happy with print outs (instead of hot off the press books) there are a number of wonderful websites:
There are two more websites that, while not specializing in anarchist writings, have an enormous selection of anarchist essays, texts, and books (both require registration but they are worth it!):
Lastly, torrent websites can sometimes turn up something of interest:
(or less worth while:)
There are many other good places on the interwebs but this should be a good start.
For free printing:
If you find out the models of network printers used on a campus and download the appropriate device drivers before arriving, sometimes you can bring a laptop from home into a campus and plug directly into their network device and print for free (just do it at a time when you won't noticeably disrupt network traffic provoking a visit by someone who maintains the network).