I'd expect about 24mpg on highway for V6 and 20 mpg for V8. Those are estmates, depending upon how you drive, lots of hills where you live, etc.
And the V8 might need premium gas, not sure, which costs more.
At 20 gallon tank, expect to spend $60 to fill gas tank, at $3/gallon, or only $40 per tank at $2/gallon.
So it'd be better to get a Toyota Corolla and get nearly 40mpg, double the mpg of the 4Runner.
