That's certainly right!
I drive an S15 which is only a 2ltr (turbo ) and I get pretty much 370 - 400km's a tank on ultimate 98. Granted, I have a heavy foot on occasion.
Don't forget about everything that goes with a car though mate.
1. Car repayments (Should you ahve finance)
2. Insurance (Don't even think about not having it)
3. Fuel
4. Servicing
5. Consumables (Oil, Pads etc)
It all adds up.
Think of it this way. The car will cost you bulk dollars, trust me I am 18 and I am feeling the cost of car already but its worth it