Clyde,
There are several programs on the market and free from websites. Some of them work great and have documentation to review. Some don't offer support and expect you to do trial and error to get the control to communicate and find your own hardware interface to the equipment.
If you want a few options, such DNC Software and check out each site, talk to the reps, ask your machine tool guys, CAM company, and other shops. Each will tell you a story that might lead you to a few vendors to chose from.
I have been in the market for 15+ years and they all can communicate, but at the end of the day, how much support, service and upgrade path do you want for the future. I can't tell you how many shops I walk in and see 20% of the machines not setup because they could not get it working with the free stuff. They say, nothing comes for free without a price (paid in time, effort, lost productivty, or ??).
Check out our solutions since we offer eXtremeDNC and Predator along with hardware products that do not require software. It generally gives you a good idea of cost and then you can check out what others say about the solutions.
Greg Mercurio -Shop Floor Automations
www.shopfloorautomations.com /619-461-4000