Dealers were pricing used units to me for ~$30ea or so.
If you are the adventureous type you may want to try one from a later optioned 72 model Imperail or other car. NOS units can still be found and are dirt cheap. They are smaller than the 70-71 units. I was told they could work as replacement. I would have to look but I think the original had 4 leads and the later model had three. It was explained to me that one of the ground leads was omitted in the later model.
LMK if you want a part number - in fact I ended up buying a complete setup from Aloha so I never tried it. You can have it if I can find it