Automated offer lookups on Amazon

I have (mis)spent countless hours looking up used prices on books and CDs over the years. I need a way to take a list of titles, ISBNs or UPC/EANs and getting offer info automatically.

Where to start? A web search for "amazon seller api" led to Amazon Marketplace Web Service (Amazon MWS)

However, this is only available to pro merchant accounts, and since we sell way less than 40 items a month, it doesn't seem like a good investment.

Does that mean going to some hand-rolled screen-scraping app?

Then there's Amazon Web Services (AWS) which seems to have been replaced by:

Amazon Product Advertising API
which is a way to get info I want. Ah, but the terms of use say that I have to submit an enrollment form stating how I intend to use the API to drive sales to Amazon, which is not my goal.

Hmmm.

Looks like we're back to screen-scraping.

Well, whatever.
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AWS ISBN lookups

According to
http://developer.amazonwebservices.com/connect/thread.jspa;jsessionid=60DB095B0716D304492219731874FBC8?messageID=21917喝


http://xml.amazon.com/onca/xml3?locale=us&t=[amazon-id]&dev-t=[token]&AsinSearch=[isbn]&mode=books&sort=`+pricrerank&offer=All&type=heavy&page=&f=xml

Alternatives to Amazon API:

isbndb.com