What Windows 7 to purchase to correct blocked key?

Last year I purchased a retail copy of Windows 7 Home 64bit from what I thought was a legitimate seller. About a month ago, Windows begain saying it was illegal. After some troubleshooting and calling the Microsoft Activation Desk, I learned that the key had been blocked by Microsoft for software piracy.

I would like to make the install proper again (legally). I have put a lot of work into the install am hoping that I will not have to start over again...but I also would prefer to not have to pay hundreds of dollars.

From what I have learned, a retail OEM copy should allow me to just perform a key change without reinstalling, but copies are pretty expensive. Otherwise, the only other option seams to be is to purchase a digital license and do a complete reinstall.

Do I have any other options?

Thanks for any advice you can give.

@RolandJS: I did check the Altex Electronics web site and they do not have Windows 7 advertised for sale...but I probably would call them if it comes down to me looking for a physical copy. So thanks for the info.
@AddRAM: Thanks for the help

AddRAM said:

He needs Home Premium

Amazon.com: Windows 7 Home Premium

I think Amazon backs up everything they sell, but I still think you`re taking a chance.

And you are correct, all you need is a legitimate key to activate your current install.

This is where I get confused and a bit nervous (which is why I decided to post here). So any valid key will can be used to perform a Key Change on a previously installed system? I read in a few places that some keys require a fresh install (such as system builder and digital download keys). As I mentioned above, I was getting the impression that buying a retail box was the only way I could go. Of course, if there is a more affordable option that does not require a fresh install, I would probably jump on it.