I've always wondered how much would the price of a car/truck decrease, if advertising for vehicles would be banned? 10%? 20%? 30%? And if they authorized cars

I've always wondered how much would the price of a car/truck decrease, if advertising for vehicles would be banned? 10%? 20%? 30%? And if they authorized cars to be sold outside of showrooms, how much would they drop further? It seems to me that a huge portion of the price winds up paying for advertising + the showroom building + the salesperson and their administrative staff. I hope one day we can go from factory -> consumer without all this extra cost baked in.