Lowes is selling the GE (COP=2.2) for $1599 and HomeDepot is selling the Rheem (COP=2.0) for $1499. AirTap also makes an aftermarket unit that you add to your existing water heater. It's $700:
http://www.airgenerate.com/
PS. I forgot to mention that they all qualify for a tax credit of 30% of the price + install costs in 2010 only (US).
Consult your tax professional. :-)