The price of gas or diesel fuel is liable to go higher due to happenings in the middle east and American politics. Cost of fuel is a small part of the cost of ownership and usage of RV's. Many ignore the costs and see camping and touring as "priceless". Comparing cost of owning, using and maintaining including DMV, insurance,storage if required, to driving a car and staying in motels, etc are like comparing apples and bananas. If you can afford it and will actually use and really enjoy the RV often, it may be " worth it". It's a truck full of appliances and electro-mechanical stuff that becomes a hobby in itself to maintain,more like a cabin cruiser than an SUV.
Read the FAQ's at the top of this forum page and search "miles per gallon", for more info.