[ldolse]

Ah, think I found something interesting here. From this ISBNDB URL:
http://isbndb.com/data-intro.html

example data message:

<?xml version="1.0" encoding="UTF-8"?>
<ISBNdb server_time="2005-07-29T03:02:22">
 <BookList total_results="1">
  <BookData book_id="paul_laurence_dunbar" isbn="0766013502">
   <Title>Paul Laurence Dunbar</Title>
   <TitleLong>Paul Laurence Dunbar: portrait of a poet</TitleLong>
   <AuthorsText>Catherine Reef</AuthorsText>
   <PublisherText publisher_id="enslow_publishers">
    Berkeley Heights, NJ: Enslow Publishers, c2000.
   </PublisherText>
   <Summary>
    A biography of the poet who faced racism and devoted himself
    to depicting the black experience in America.
   </Summary>
   <Notes>
    "Works by Paul Laurence Dunbar": p. 113-114.
    Includes bibliographical references (p. 124) and index.
   </Notes>
   <UrlsText></UrlsText>
   <AwardsText></AwardsText>
   <Prices>
    <Price store_id="alibris" is_in_stock="1" is_new="0"
           check_time="2005-07-29T01:18:18" price="14.92"/>
    <Price store_id="amazon" is_in_stock="1" is_new="1"
           check_time="2005-07-29T01:18:20" price="26.60" />
   </Prices>
  </BookData>
 </BookList>
</ISBNdb>

Note the last sections checking amazon for stock. If it's new & in stock at Amazon that's the most current version that would have the best cover to scrape.

Looks like you need to add the 'prices' argument to the isbndb query:

/api/books.xml?access_key=Z&results=prices&index1=isbn&value1=0061031321

More info here:
http://isbndb.com/docs/api/51-books.html