It all depends on what you have. In my experience, don't expect more than maybe $5 per book IF they take them back.
I'd like to add that every time I've done it the person behind the counter has been a total impatient, pretentious snot. "UGH! We have about 1,000 copies of this book" "There's a crease in the bottom corner of the back cover. We only take books in excellent condition" Just understand that they may only take half of what you bring in.
"If this is going to be a Christian nation that doesn't help the poor, either we have to pretend that Jesus was just as selfish as we are, or we've got to acknowledge that He commanded us to love the poor and serve the needy without condition and then admit that we just don't want to do it." -Stephen Colbert