I'm looking for a database of current textbook values.

If you go to one of the following sites:
- http://www.textbookbuyer.com
- http://www.textbooks-4-cash.com
- http://www.sellusedtextbooks.com

and search with textbook ISBNs like:

0838406777
0321021738
075067069X

they provide prices at which they are willing to pay for textbooks.
Interestingly, their prices are all close regardless of the type of
textbook.

According to http://www.sellusedtextbooks.com/affiliates.html, they
have a "database of over 50,000 titles." Instead of searching on their
websites, I would like an actual copy of a similar database with
50,000+ books (and one that has prices that corresponds closely to the
buyback sites).

MBS Textbook Exchange seems to have one:
http://www.mbsbooks.com/Wholesale/Database/

Is there a free version online? If not, can I obtain access to such a
database for under $100/year?