I just bought a used IBM 6094-030 Spaceball ($25 + $9 s/h). Ebay has about a dozen of them listed.
I downloaded the 2003 driver from :
http://www.3dconnexion.com/downlink.asp
Got it running with no problem. I got it for Inventor, but there is also a driver that works for Autocad. Great for 3d rotation and zooming.
Does anyone know what advantage the new $300 models have over this model.
Bill