@PotomacBob
want them to try to duplicate what it was like to travel in the U.S. before there were interstate highways or credit cards or ATMs or bank cards or Holiday Inns, is it doable?
Whole new can of worms.
Two young people traveling across the US without cards of any flavour, avoiding interstate highways. Sounds like a wonderful adventure to me.
However, that requires them carrying large amounts of cash, whilst I'm not suggesting they need a gun, they certainly risk attracting attention, it would be all to easy for someone to overhear a couple of comments, put two and two together and hey presto, rob them, either forcing them to hand over money or robbing their room, car, bags etc
So, whilst the experience of the trip you propose would no doubt be a wonderful adventure, the reality could well be far less enjoyable.
If you do go ahead, perhaps agree an itinerary and prepay the hotels etc in advance, leaving them only food and fuel to pay in cash, less to carry and if the worst happens they at least have somewhere to stay.
Having said that a friend crossed the US coast to coast before going to Uni, with just over $500 a backpack and a thumb to hitchhike. She enjoyed it very much, was spoilt, scared stiff, lost and propositioned, but has enough stories to last a very long time.
So yes, it is possible, but 'caveat emptor' so to speak.