Personally I was in a similar situation to you(though I'm staying with manual milling for a while) and I decided to go for the Grizzly G0704 Mill instead. The cost isn't much more than the SIEG machines, but it has a lot more capabilities and is much more rigid.
http://grizzly.com/products/G0704 Just something to consider. There's also plenty of info on the web for converting these over to CNC. Also look out for a few other companies that also make this machine such as precision matthews.