For my Dieselpunk RPG I use old copies of the Sears and Roebuck catalog for most pricing but I still need a good resource to determine the cost of the cars and motorcycles of the era/s.
Does any one have a good resource to pass along?
That's a tough one. Are you looking for specific years? I can find a few individual ads but this could take quite a while and is likely to miss years and models.
The best document to have would be price sheets from dealers in certain years but auto dealerships were so convoluted as to which cars they could or couldn't sell you'd never get a comprehensive idea of pricing. There are tables for manufacturer cost by year but only for Dodge and Ford. The best resource I have now is the Daredevil RPG rules.
As you say, auto dealer prices are intentionally convoluted even today. Not to sound like a cheesy gamer but this sounds like an opportunity to create a formula from these ads and roll dice to wheel&deal the car salesman up or down. Used cars will be a much greater price range but you never know what will be available.
Notice that there were apparently car modifying shops then that offered fancier cars at discount prices. Sort of like kit cars today but ready to drive away. IF drivers are will to pay $45. to make a Model-T look sexy (I understand that those Speedster bodies were wood, cloth, & dope like a biplane) then what would a mobster or bootlegger pay for a specially modified car?
At the end of the day, how important is exact prices, makes, models, and dealing to an rpg campaign?