This link to a thread on pnet gives the details of an upgrade from Elements to CS3 for $300.00 :

http://photo.net/digital-darkroom-forum/00Q2I7

I had an ancient elements2 disc that came with an epson scanner -- never installed or registered-- and I called Adobe and they registered it and gave me the upgrade to CS3 for $329.00 with s&h. They even looked up the promotional code for me.

Not too shabby, I thought, since it's even cheaper than the educational discount price.