Are you selling amplifiers too? If so, get a dedicated 12-volt power supply for the amplifierss. The more current (Amps) the power supply is rated at, the better. Although PC power supplies might be ok for powering the radios.You might need several power supplies depending on your set up.
Use a switching system to power one 'set up' at a time. By set up I mean a radio, an amp an a subwoofer amp. You may also need speaker and audio switches.