At less than $2 each, you can't beat the bang for the buck using automotive 12V relays.
If you need a 12V DC power supply to drive the relays you can also get a regulated 12V DC, 1 Amp wall-wart on eBay for about $2 (free shipping). If you add a 50 cent (free shipping) adapter jack, you don't even have to splice the wall-wart cable.
1 Amp @ 12V is 12 Watts. So this can drive half a dozen standard automotive relays which require just under 2 Watts each as Dale points out. For a few dollars more you can get 2 Amp, 3 Amp, etc. 12V DC power supplies.
OGR will delete direct eBay links but here are search words and current listing #s which you can cut-paste into the eBay search box:
"12V 1A DC US power supply" (e.g., eBay # 181939256344)
"DC female adapter jack" (e.g., eBay # 252186410477)