I found out about Betterworld.com, a cool site to look for used books that has free shipping--they have new books too (usually priced a little higher than Amazon). Betterworld.com gets its used books from libraries mostly so it is for reading copies of older books not anything collectible. I was able to find a used Cath Kidston book, Vintage Style, Christmas in France by Corinne Ross, The Doll House by Rumer Godden and three Patricia Wentworth mysteries that are out of print all for about $22.00. Ya just can't beat that! :-) The free shipping part is for a 4-14 day arrival time, however you can pay to have it arrive sooner. I was especially thrilled to find the Wentworth books because they are just such "cozy" mysteries and kind of hard to find.
You can also feel good because Betterworld.com funds world literacy with its profits--find out more from their website.