Jim, we are on the same boat.You could pay 3 to 5k for a terminal that will handle 24 channels or could pick up one from e-bay for few hundreds.
Also you will use untold ammounts of hours putting it together, running into dead ends and fighting diferent issues.
But at the end you will earn a lot and be wiser.
Be aware of billing systems on e-bay. That seems to be the wild,wild west od the VOIP arena.
Only second to the VOIP providers with a very low price that ask for prepayment and run.