Looking for a bargain? Low on cash? Try your local Goodwill store for books on the cheap! Usually you'll find hard covers for less than $3 and paperbacks for even less. They have sales on them all the time, I got This Pen For Hire by Laura Levine yesterday for 25¢!
WARNING: There is no order what so ever (in my experience), so you'll have to dig for your treasure, but for pennies on the dollar and hundreds of options, who cares?!