Whatever the wholesale cost of a radio module they will pay just as much for the one without AM. They don’t want to support something most customers don’t want, and the ones that do want it will complain about interference. I knew a guy who had an old truck with no radio. Know what he did? Bought what we called back then a ‘transistor radio’, a small battery operated radio that he kept in the truck. I’m sure you could find one that you could plug into the thing that’s not a cigarette lighter.