With 3 hours of ~500 watt plug in heat, I get EV in 0.7 miles, 1.5 or 2 minutes after a start up at about 35'F.
So I figured 1.5 kwh *(20 cents in many cities ) saved me about 35 cents of gas.
But the big advantage is, it keeps my average up in the "standings" on GH.
Cost for the system varries between 2005-7 and 2008.
I've heard, but can't prove the 2008 does not come with the battery heater.
The 2005-7's get a block heater and battery heater in one package.
Or maybe the 2008's already have the battery heater part?
There are other threads on this also... pretty recent ones if you care to look.