A few years ago I got the rubber over steel tracks from McLaren,
http://www.mclarenindustries.com/. They were about $4,000 I believe, and they threw in 4 new tires. They've worked great. I just leave mine on year round. You never know when in the middle of the summer you'll get a deluge that turns a site into a mudhole. And they are a pain to take on and off.
The only drawback is that the rubber pads have worn down quite a bit and need to be changed now after maybe 350-400 hours. If I could only get my guys to stop the hard spinning that causes this! On the flip side though, the tires on the machine look as good as new, so if there were no tracks they would have just wore them out.