[IMLost]

Economy? Unleaded @ $3.10 Premium $3.50 = $6.40 per fill up if totally empty. Say you fill up once a month, $76.80 a year.
How much money are you spending on this thing?
If gas mileage is a consideration I would have to assume that you do not intend standing on it in first or second gear. Let alone over 60mph.
Build what you want and drive the **** out of it when you want to, and if you need to save money drive slowly somewhere park it and enjoy the view.