I'm not even sure it is possible to answer this as the whole industry (DIY CNC) is changing rapidly. Probably your cheapest solution is GRBL on Arduino hardware. One of the more interesting and new solutions comes from CENTROID CNC controls,CNC Milling Machines,CNC Lathes,CNC Routers,5 Axis CNC Cylinder Head Porting Machines,CNC Retrofits. Digitizing, Automatic Tool Changers, Probes, CNC Rotary Tables, Conversational Programming, Auto Tool Measurement. with their Acorn controller. That covers one of he older and one of the newer platforms for the DIY market, there are dozens of others. The problem is any platform worth its salt is under constant development so if you go looking for user experiences make sure the comments reflect recent hardware and software.
In any event there are dozens of solutions out there covering a range of price and features.