Really, the type of car has some dependence on the time of year. We live in the intermountain western U.S., and even the excellent Interstate Highway system can become difficult in the winter months. the distances between populated areas out here can be daunting to Europeans and Brits. It's 2,500 miles from coast to coast and, once you're west of the Missouri River (say, Kansas City, MO.) you can travel for 50 miles without being in a sizeable town. So, a typical standard sedan that will seat 4 adults and have reasonable luggage space in the trunk (ya'll call it something else, no?) will cost between $25 and $40 per day U.S. Generally you are allowed unlimited free mileage, but be sure to check. The larger rental agencies are the more expensive, such as Hertz, National and Avis. Personally, I like Budget, Dollar, Enterprise or Alamo. After all, they're all the same cars. Fuel is averaging about $2.80 per gallon right now, but varies weekly.
There's a brand new travel link that just started up that does a pretty good job of searching all the sites to find the best deals on hotels... it's www.TripMama.com. Travelocity is also a good one for hotel discounts. Depending on where you're staying, reservations are a good idea.
Good, name brand hotel/motel accomodations, such as Holiday Inn Express, Fairfield Inns, Comfort Inns and Suites will average about $80 to $90 per night. The higher end Marriott Hotels, Courtyard, Hilton Inns, Sheraton Inns, etc. will average about $110 per night. (The exchange rate is very much in your favor right now. Decent but lower end rooms at $50 or less can be found... caveat emptor!...Meals will average about $10 for breakfast (most hotels now offer a pretty decent free breakfast as part of the room deal), $12 to $15 for a good sized lunch and sky's the limit for dinner. Figure $18 to $25. Obviously, Fast Food is a lot cheaper...
Welcome to the U.S., by the way...