gas mileage?

ok, heres the problem. i used to want an mk3 turbo so bad, and now i found a great deal on one. its an 88, with 106k miles on it, and the guy is selling it for 2k cuz hes out of a job. the only problem is that now im working construction and i drive a lot to get to work. what kind of mileage can i expect with these cars if i switch gears before the turbo kicks? of course im going to play around with ti every now and then, but not all the time since gas is supposed to get expensive. whats the mileage with low shifts? if you use the turbo? thanx

17 mpg street
22 mpg freeway

with normal driving.

All i know is when i play with my TT the gas literally is draining out of my tank.