Audi A3 8V 5F fault

Hello, I am after any quick advice someone with experience may be able to give me. I have a 5F fault resulting in the MMI system being totally dead. My local garage has told me this and suggested it requires Audi Dealer diagnostics, which I totally understand. My question is does anyone have rough ballpark figure for what this fault might cost to fix? Reason I ask is my car is 10 years old on 170k miles (I've done them all). The engine is rock solid, but if I choose to repair the MMI it will only be to sell it. Value on mine is probs around £3k, so if the MMI costs more than that to fix I'll not waste my time. Main dealer want £99 to run diagnostics, but I don't even see the point in paying that if the repair is likely to be near the value of the car. Sounds like I'm being tight, but I have spent a fair bit on it recently and reached the point where I will buy a new car. It's whether I choose to get £3k for it repaired or just bin it. Any one got any advice on likely cost? It would be very much appreciated.