Most people don't buy Mustang SVO's because of their reliability or gas mileage, but because they represent a unique, limited production car, which at its introduction to the market, was certainly at the cutting edge.
2.3 turbo engines and drive trains are extremely rugged and can easily withstand HP levels at over twice the factory figure. The have forged rods and pistons and use a valve material, which can withstand high temperatures. They are fairly easy to diagnose and repair and parts availability is as good as you will find for a 1986 model car. Realistically, you can squeeze over 20 MPG out of one in combined city/highway driving.
Having stated this, I would never destroy this car by using it as a daily driver!
Mustang SVO's will be very valuable someday and driving one into the ground on a daily commute would be a ridiculous waste. If you buy it, treasure it, maintain it and keep it as an investment. The rest of us 2.3 Mustang junkies will look at it in envy and you will own a unique piece of American automotive history. If you are looking for an economy car, there are far better choices out there.
TVS Supercharged SVO 2.7L
561 ft lb