Bookcloseouts has an interesting new sale section on their website. They now have 50 books discounted by an additional 50%. This 50/50 section will have a new 50 books every 2 weeks, so you’re going to want to keep your eye on it. You do have to pay shipping but I have always found it to be reasonable.
Click here to check out the 50 for 50 section at Bookcloseouts.