You can create DC easily from an available AC source, taken off one of the ZW outputs, or you can use a 12 volt junk-pile wall wart from various small appliances or gadgets.
Altronix model RB1224 is an easy-to-use example of a relay. They are cheap and can usually be found on Ebay for less than ten bucks. A diode bridge (a dollar) and a filter capacitor (a few dollars) will be all you need.