Mach3 is a great program and is actually repackaged and dressed up by a few other companies that offer cnc control software.
I understood the initial question from the OP as they already have general cnc control software and are looking for a cheap 3D solution? if I misinterpreted that and they are simply looking for a cheap general control software without a doubt Mach3 is the way to go.
I am reluctant to recommend Mach3 to users who really don't grasp the overall concept of how 3axis routers work. If you are not of a mechanical thinking mind and simply want to view your image on the
computer screen, push a button and watch your router run in my opinion you need to invest in a more user friendly software package than Mach3..even with Lazycam it requires an operator that 'gets it'.