Controllers-the missing link

So far this ia what I've come up with for my project to add cnc to my
Smithy Granite.

1. Hardware and mounts for a belt drive system
2. 450 to 500oz stepper motors in the NEMA 34 size
3. Stepper motor drivers rated for selected motors
4. Unregulated DC power supply appropriately sized for motors and
drivers.
5. Controller, signal generator ?????????
6. CAM software
7. CAD software
8. PC

I'm starting to get a feel for the steppers, drivers and power supply
but the controller is still somewhat of a mystery. I see there are PC
card systems, external systems, CAM software with controller cards
etc.

Being a total newbie to cnc how do I sort out what I need? My cnc
purpose is purely hobby oriented and since this is my first attempt I
want to keep the costs a low as possible and still get an adequate
system.

Jay