All:
In addition to the dollar cost of purchasing the software, there is the "cost" of learning how to use the software. Some software is easier to use than others. I've never used any of the software above, so I can't comment on the number of hours required to learn each of the packages above. I suspect that it is tens if not hundreds of hours, tho'. Perhaps Dave can comment on the software learning curve for each package.
Also, all the CAD and CAM programs are constantly being updated, so you have the constant decision "should I upgrade, or not?". (This is very similar to the "If I had the Shereline's ABC attachment, then I could do XYZ" dilema that constantly crops up.)
Lastly, figuring out how to get all this software to do what *you* want it to do can actually be a bit challenging. For people who have been doing it for a while, it is easy. For the first timer, there is a dizzying array of strategies where some strategies work better than others.
Let me be a little specific here. In CNC there is the concept of "speeds and feeds". "Speed" means spindle rotational speed and "feed" means the rate at which metal is removed. When you've got a chunk of metal you've got to figure out both speed and feed values before you can successfully use your CNC mahcine to cut the metal. If you get your speeds and feeds wrong, you get horrible noises, lousy holes/edges, broken too bits, etc. It takes a little while before you figure out what speeds and feeds work for *your* machine. If you go to the Shereline CNC list and ask "What speed and feed should I use to cut 6061 Aluminum?" you are more likely to get a lot of hemming and hawing than a straight answer.
Again, I do not want to discourage anybody; CNC is a great deal of fun and can be wonderful adjunct to doing robotics. Indeed, I view a CNC machine as a robot that just happens not to have any mobility.
My $.02,
-Wayne