I dunno about if its a scam or not but I once bought a win7pro key for as cheap as $40 CAD from microsoft because of a student discount (comparative US price at the time for the deal was $30 USD) I bought it directly from Microsoft of course
So it can be really cheap sometimes
The site is run by some Chinese dude in case you're wondering (assuming from the email)
http://whois.domaintools.com/win7productkey.com
EDIT: IT'S A SCAM
http://www.technonsense.com/2011/02/cheap-windows-7-winkey-sale-scam/
http://www.scamadviser.com/check-website/win7productkey.com
Run Linux until you can save up