I installed myself heated seats in my car. Installation set, heating pads, switches, wires and relays for two front seats was $56. I would say it costs manufacturer $10/seat.
JOOI, can you arrange to only pay when it's cold enough to need them, or is cancelling/resubscribing the huge pain one might expect from such a scheme?
"Heated seats" is just a piece of wire put into seat, some $1 (probably less) micro to turn it off and on and some $0.1 sensor.
I wouldn't be surprised if even few % of buyers buying that would cover for having to fit extra (and not have separate SKU for heater-less seats)