MOI, is free; http://www.moi3d.com
Rhino; http://www.rhino3d.com, is reasonable.
Both Rhino and MOI have a learning curve and you have to build everything you need using MOI, there isn't any libraries of settings, stones, shanks etc. Rhino has some stuff available aftermarket for jewelry, but since I don't use it, I'm not real familiar with what's out there.
3Design; http://www.3designjewel.com, is @ $6,500 and is better than Matrix, IMHO. Easier to learn and has a history feature, so if you change an element in your design, say stone shape or size, all the other elements of the design adjust to fit. A great time saver.
If you have time on your hands, mess around with MOI, or buy Rhino, but it'll take some time to become proficient. I've used Rhino some and have clients who use it and I'm not real fond of it, it's a bit clunky and quirky. There are tons of users out there and good forums, so there is plenty of help. It is a good value too, as it's reasonable.
Spend the money on 3Design if you want to be making and selling pieces instead of spending all your time trying to figure out the software.
Good idea to hold off on the CNC part of the equation, there's plenty to learn with CAD first before adding that to the mix.