I've lost the receipt but it was about $35 for some interior trim, a wire harness and heating elements at the local pick-n-pull.
somewhere in there, I'm guessing maybe $10? + $5 for two stock switches from the same truck.
I think it would be a much bigger deal trying to replace the upholstery on some JY seats. I'd also be worried about mold already growing in the JY foam.
The easiest route would be to pull the heaters. maybe take some dimensions and look around at other Nissans. You might find something you don't feel so bad about tearing into.
Put the heaters into your own seats.
check your rig beforehand to see what harnesses you do/don't have.
the connector I ended up using to the M70 line was also tied into a few other harnesses, including the main harness which I would guess runs most of the stuff behind the front seats (rear speakers, tail lights, r. wiper, fuel pump, etc.) the heating/power/side airbag harness is NOT separate from these other wire looms.
Since I didn't explore this option too much, I don't know what would be involved in retrofitting the sub-harness for the seats.
The neatest way I could think to do it is trace the wires from the pass. seat heater back to M70 and try to get those actual connector terminals out of the connector w/o breaking anything (or break something, it'll be crushed in a month anyways). Then they'll just clip those into the connector you already have in place; assuming yours is set up like mine. Then just tape the wires to your stock harness.
But again, check what you already have in place, if there's ANYTHING powered on the passenger seat (seat belt warning, air bag, power adjust) you might be lucky and already have the connector ready to go.