Is your wording this poor all of the time?
Yes, the difference will be more than that. However it will NOT be the $30 you stated earlier. And the difference in fuel economy will mean MORE frequent fill ups, not a 50% increase at EACH fill up....
geez.
And as I said earlier, if you're purchasing a new car and the $100-200 more you will have to spend on gas a month will break you, you shouldnt be buying a new car...
To be fair, many vehicles get about the same range, and the fuel tanks are larger in lower mpg vehicles. So the frequency will be about the same (based on miles driven), and the cost will be 2x as much (given the 15mpg and 30 mpg examples) to fill up the larger vehicle vs smaller, given that the range is the same, which means the fuel tank is twice as big.