cheapest radio transmitter and receiver for Canon 5D2 to 580EX ??

What would be the cheapest radio transmitter and receiver for Canon 5D2 to 580EX that would be fairly reliable for use of maybe one hour a month at most? Will be used outdoors with stand and umbrella where no outlets available for my 2 AB800s. I very much appreciate any help.

-Gordon-

--
'Who loves yah, Baby?'
... Lt. Theo Kojak, Manhattan South