2003 Audi Quattro Oil Indicator was on and after machine r

Hi,

I got a 2003 Audi 1.8T Quattro with 50K miles on it.
About two weeks ago, the oil indicator on the dashboard was on. But after we restart the engine after a while, the oil indicator was no longer on. After a week, we took it to the dealer for a regular maintenance. Just today, the oil indicator on the dashboard was on again. We took it to the dealer for diagnostic check, they ran it, found nothing. But I guess they wouldn't want to be responsible if anything was wrong, so they suggested further testing and that the car is not safe to be driven because if the problem lies in the oil pressure then if we drive the car, it would ruin the engine. They recommend further testing for $600 to take apart the engine and do a manual test. Can anyone help us? Can this really be a symptom of a problem with the oil pressure? If yes, is there a cheaper way than $600 to diagnose it?