Burrrrr! That's too cold to work! I have the same heating system in my shop and it's expensive when it's really cold.
For a basic controller system, all you need is a standard computer, your choice of monitor, a keyboard and a mouse. Add to that a motion controller that will output a +/- 10V analog signal to your servo drive amps, and software that will run the whole thing. Beyond that the sky is the limit. In your case I would use the existing servo motors and amps (drives). They are very robust and trouble free.
Mach3 is probably the most popular controller software, is pretty well supported and cheap. For a motion controller, Galil Motion Control products are my preferred systems. Galil plays OK with Mach3. Currently the Mach3 Galil plug-in supports both Ethernet and USB connections, as well as PCI bus connections with Galil. Last I heard, they are still working on the Mach4 plug-in for Galil, and it was not ready as of about 6 months ago.
These are the current top-of-the-line controllers Galil controllers
http://www.galilmc.com/motion-controllers/multi-axis/dmc-40x0
http://www.galilmc.com/motion-controllers/multi-axis/dmc-18x6
http://www.machsupport.com/software/
There are a number of used Galil controllers available on Ebay, but know what you buying. I will be happy to help evaluate anything you find.
We installed Mach3/Galil on Alloy's Shizouka AN S, it works OK for all normal machine functions, but I'm having some issues with the tool changer functionality. Had it running G-code within about an hour of firing it up the first time.
http://www.hobby-machinist.com/threads/shizouka-an-s-build.33868/ This build is crazy complicated and not a normal conversion. We started with a blank canvas and built the entire system from the ground up. Includes a 24 station tool changer, and a very strange spindle speed control system. I did the design and programming, and Alloy did all the work
On the other hand, I did the conversion on my machine right in the middle of a job when one of my encoders failed. About 12 hours and I had it up and running again. Didn't even take the setup off of the table. My software is absolutely free, but it will only work with Galil products, and will only run on WinXP until I figure out the comms for later Windows versions.
There are a number of other options available, most are expensive IMHO, and I don't know much about them.