If you include the cost of the RV then RVing is more expensive than a car and motels. Campsites are usually cheaper than motels but it is a lot better sleeping in your own bed each night. Meals you cook in the RV are cheaper than restaurant meals, and possibly healthier. Gasoline will be more expensive depending on the RV. Motorhomes will get 8-10 mpg. If you tow a car, the car will get much better mpg than the MH but equiping a car to tow can be expensive. If towing a trailer, your towing MPG will probably be better, but the gas mileage sight-seeing in the tow vehicle will be poorer than a car.
Whatever you decide, enjoy your travels.