Try Bergwerks they have aftermarket seat heaters that fit under the upholstry. They cost $90 for single temp and $150 for dual temp, that should be a lot less than new leather. They claim that they should be able to fit any car. Try here
http://bergwerks.com/seat_heat.jsp

I have no connection to Bergwerks and dont have these heaters but they seemed to be a good deal for an upgrade for those of us that dont have seat heaters.

Paul