Cross- country flights
A Flight is often the cheapest and quickest option to travel in the USA depending on how far in advance you make the bookings. If you book your flights enough in advance then you may get some really good deals. Depending on the season, flight rates can get high.
Bus
Traveling on a bus is one of the cheapest modes of transportation. Bus carriers like Greyhound stop through most of the cities and so there are multiple options for you to plan your trip. But one drawback is that it will take hours to reach the next destination, on average approximately 3 days.
Train
Amtrak serves train passes with various flexibility to choose your route over a 15, 30 or 45-day period. You will get over 500 destinations to choose from plus you will be able to ignore the on-road traffic.
Car
If you have a chunk of time to explore and road trip to the coast then driving by yourself by renting a car is a fantastic option. This option is not very pocket-friendly but will surely offer and experience you have never had before. Depending on the distance fuel is going to be your major expense in this case. And after that, once you add your accommodation and food costs, this is costlier in comparison to other options.