Google "freecycle" and join your local email list. The odds of you requesting and getting an EC text is slim, locals likely are using local texts, however- you never know!!
Use EC's unofficial student websites/forums. All colleges have them, and usually textbook swapping is a major activity! I have no doubt this is an excellent way to get reduced cost books.
The publishing sites (Wiley for example) often put their current edition's support site online. These are tricky to find- but usually this are not the same sites that you need an access code for. Anyway, find your book's site. It will be worth gold. Combine this with an older edition of the text and you'll be good to go.
There are actually online text books for free. I used to have a couple links saved, however that computer is long gone. I don't have the time to hunt for it, but I will tell you that "yes, there are" so I encourage you to start googling.
Library - excellent suggestion. I want to underscore that libraries are linked electronically now. So, go to your local library's web site. Type in your text, and if it is found- simply do a request. Someone suggested it was $1, but my library still has no fee for this. Also, if it isn't found, drive down to your local library and request the book. My library has (at least 4 times) bought the book for me.
My husband's last text through our library was an electronic version by the way- so he simply logged in from home to view the book online.
College bookstore- Believe it or not, colleges often throw away books that they can't sell. (I know- insane). After 17 years working for a community college, I can't tell you how many books get tossed in the trash. (hundreds per semester). I'm not suggesting you dumpster dive, but you could also tactfully ask a worker (not manager) when they discard books. Ours is usually twice per year. Our bookstore places them in the hall, and generally, students just take them- so few end up in the actual "trash" but I have obtained my AP Lab manual, chemistry molecule snap together set, dozens of biology books, nursing books, math books, etc. I list this option last because the odds of you getting the exact book you need are slim- but, if you can find a book that is helpful, you might grab it just for future reference.