I wish you luck on your attempt at a road trip! My friends and I did one this past summer after graduation, and it was awesome.
My parents were against it at the beginning too. What my friends and I did (and what I think was a big factor in their decision in letting me go) was compile an itinerary and calculate all of our expenses. We did a breakdown of everything we planned to do, estimated of how much we would spend on food and gas, and put it all on paper. We provided the contact information of everyone going on the trip as well as the contact information and address of the hotels we were staying at and where we planned to go (like, we planned to go to a comedy theatre, so we put down the theatre’s address). And we actually overestimated how much we ended up spending too.
