There was a time when old software was transferable, but because of license verifications and upgrade procedures, the company must usually maintain the original software as proof of licensing for updates/upgrades.

For Autodesk, there are "light" versions of some of their software that have most of the functionality without the full cost.  For instance ACAD Light.

Check with the company on its policy for old software licensing.

Also for AutoDesk, they have very punitive contracts with value-added software developers (like COADE for example) that precludes the value-added guys from supporting software more than 3 versions old.  I had a copy of AutoCAD 2006 that was working perfectly and doing everything I needed it to do.  COADE came out with their 2010 version and I couldn't install the latest version of CAESER II because my AutoCAD was too old.  I finally decided to "upgrade" to AutoCAD 2009 and have regretted that decision ever since (everything is just enough different to be annoying).  My point is that there are certain pieces of software that are core to a business, you need to build that list VERY carefully to make sure that if something like CAESER is key, how important is it to have the latest version, and can you afford the ancillary costs.

The ESRI stuff is easier, nothing much is tied to them and a significant portion of the user community is using very old software successfully.  I've been paying the maintenance fee for 7 years, and realized that their "upgrades" have not added any value to me for several years and cancelled the maintenance.  It is such specialized software that I would be surprised if you can get a deal on an old copy.

David