The best search aggregator I've found for books is bookfinder.com . It pulls in prices from Abe, Amazon, Alibris, Biblio, Ebay, Zvab, and possibly others. You can specify used or new, hardcover or soft, editions, and publication date range. Prices are sorted lowest to highest. I also use worldcat.org to locate library holdings and/or search for copies to read online (or download).