Honestly I would recommend NOT buying a Class A if your budget is $4k and you are worried about gas. A class A is not for everyone and not for every application. With your budget you are going to end up buying someone else's problems and the cost of maintenance is going to kill you.
Consider these options:
Option 1: Buy a tent trailer and tow it with your car/van/truck. It will give you clean, dry camping at a low cost. There are plenty of inexpensive options for you.
Option 2: Consider buying a conversion van. It will have a TV, a bed and a refrigerator in it. The cost to buy is within your range. The gas mileage is better. They fit everywhere.
Also as a last option you could consider a class B motorhome. Smaller, cheaper and better on gas.
