Have a look at the vectric "vcarve" offerings, vcarve pro is an excellent CAD/CAM package, very easy to use, well designed and powerful. They do a free demo you can try with the machine and while you can only cut their supplied projects, you can use the demo to do a bit of design and see how easy (or difficult) it is to do what you want. It is quite expensive (and aspire for full 3d is even more so) but I'm a tight Scottish git and I've never regretted buying it.