What kind of mileage can I get?

[finaltable]

I was offered a promotion at my job last week; the downside being that I will be commuting about 70 miles round trip each day. Last time I faced a commute I bought myself a Mk III. It appears that it is time for another. I don't care about going fast; I like the look of the car, the confident push of rear wheel drive and the targa roof. I know cars can be modded for power, I am curious to know if the car can be tuned to be more efficient. I have access to a mechanic (my uncle) who will be happy to help install anything I need, even a 2JZ engine swap if that would help. I am open to any suggestion that still makes the car look and sound professional, e.g. no stripped interiors or fart cannon exhausts. This to be a touring car, not a street racer.

Thanks