You can get the Watt Meter & Power Analyzer /Watts up from Hobby King for about $40:
http://www.hobbycity.com/hobbycity/s...idproduct=6380
Or, you can build this one for about $3.00: Mini-HowTo - $3 Wattmeter
http://www.rcgroups.com/forums/showthread.php?t=949923
Bill