Being able to procure good quality, economically priced, books is always a blessing.
A while back a friend put me on to the better priced and second hand sales books on Fishpond - for us to not only purchase good finds, but onsell our surplus items too.
The added bonus; postage is free.
If you search for an item, I'll select Writing With Skill, Level 2: Student Bk by Susan Wise Bauer, and toss this simple visual up to explain. (Someone pointed out that you'd need to type in Susan Wise Bauer to pull up her listing on Fishpond.)
I've also noticed that items I've been looking for, and tucked away in my wishlist, start going down in price the longer they are on Fishpond - I think this may just be on the items that people box up and send into Fishpond to sell on their behalf - which is a wonderful purchase for the buyer, and no doubt a loss to the seller.
ALL the items we've purchased off Fishpond, this way, have been very good quality... and I'm particular.
Happy browsing: and no, I don't have affiliate links with Fishpond.