Here's what I'd do. Hit up home depot and get..
And this thing will only cost $700 after the tax credit. Shouldn't take too long to pay for itself.
Two of these:
http://www.homedepot.com/p/Watts-3-...ater-Connector-FFSS-18/202255005#.UqT0uSeQOLY
Two of these, or whatever matches your CPVC diameter and the thread on the water heater hoses:
http://www.homedepot.com/p/NIBCO-3-...ition-Adapter-C4704-CT/100187109#.UqT0ZSeQOLY
Also CPVC cement.
When the tank's drained, cut the CPVC halfway up the pipes attached to the hot water heater - use a proper cutter as domon suggested, or mark a circle around the pipe with a piece of paper and a marker and carefully use a hacksaw. Weld on the new adapters. Pull the heater out, put the new heater in and make the connection with the flex hoses.
This assumes the heat pump heater has both connections on the top.