When you are deciding on what kind of CNC servo control electronics to buy, your choices will fall into one of three basic catagories

1. Complete CNC control system like a Centroid or others

2. PC or stand alone motion control card like Galil

3. Low cost step and direction controller like Servo Lite

The first option is not really an option for most home CNC enthusiasts due to the cost.

The second option of using a PC control card for control is a workable solution that will provide silky smooth motion but it will not be cheap ether and software to run gcode will cost a lot.  If you go the PC card rout you will also need to purchase amplifiers to amplify the signal coming from the control card.

The last option of using step and direction hardware is by far the least expensive to set up but does not have quite the performance of the other choices.

Centroid Controller

Galil DMC1700  3 axis $1895  3 Amplifiers                 $600

Servo Lite