Len,
The car would not still be under warranty?
I bet that heater unit is very pricey though. I would not be surprised at all if it was four digits.
Regarding the voltages, it is probably safe as a DIY job, but probably a whole lot of disassembly required. Relays cut the high voltage off at a point inside the pack when the car is turned off. Also, DC from a battery pack in not like AC. In the case of high voltage AC, the whole Earth and anything connected to it is at ground potential. In the case of high voltage DC from a battery pack, only the packs negative terminal and anything connected to it is at ground potential. You could grab the positive voltage of the pack all day and nothing would happen. You would need to grab both positive and negative to do any damage to yourself. And unlike 12 volt systems in IC cars, high voltage traction power never connects the vehicle frame to traction pack negative - for fairly obvious reasons.