I think you are unlucky Paula, but I may question where you've been taking the car to date, and the competency of the mechanics, especially given 4 mechanics have looked at the car to date. At this age and mileage I wouldn't be taking it to a main Audi dealer and paying exorbitant labour rates, but seek out VW/Audi specialist with lots of positive reviews. Check with friends and family too if in doubt.
So Audi Q3 2015, not identified engine, but to be honest it's not critical. You've put 70k miles on it since you've owned it, so in that time you should have had a few services, I'm hoping oil services every 10k miles, plus timing belt and water-pump, etc.
First things first. The issues are fairly mixed, and will range in price from a few pounds to a few thousand unfortunately.
So your car is 2 wheel drive, however with Haldex fitted, it will engage traction control on the rear wheels so you have 4 wheel drive if the car senses a lack of grip. This is found on S3, TT, etc. The Haldex unit requires servicing.
Now, not sure if this is just Audi, but on VW, then there's no specific requirement to clean the mesh filter on Generation 5 Haldex units (which yours will be). It's preferable by folk in the know, not only to drop the gear oil, but to clean the mesh filter on the pump. I think VAG (Audi/Volkswagen) recommend every 40k miles, but Volkswagen subsequently changed this to every 3 years regardless of mileage. Ironically I think Volkswagen don't even recommend the pump mesh is cleaned, they simply drop and refill the oil. I assume Audi is exactly the same. Your service paperwork may say differently.
If the pump filter is clogged, then it can burn out the pump and in turn - it burns out the electronic module as it draws too much current trying to pump fluid through a blocked mesh screen. You would need to determine if the module and the pump are both damaged. A VCDS scan should be able to read any logged DTC errors. If it's the module only - then new they are over £1k depending on specific part number. Again I don't know if component protection is fitted?
Watch this. Dave Sterl is old-school, but he knows his stuff.
In terms of headlights, if Xenon gas discharge, then headlight is circa £600 new. If it's LED, then unfortunately it's over £2k. You can search under LLL Parts for more details based on your chassis number. Mechanics will be reluctant to fit used parts as it won't be plug and play. Audi have component protection enabled, and it's not something that you can over-ride even with VCDS, then you get into removing the coding with dealer only software like ODIS.
Rear level sensor (will be located on rear suspension on passenger side. Electrical or mechanical - usually fails or corrodes. It measures weight of rear axle so headlights don't dazzle if the car is loaded. Again - usually straight forward to replace.
4 washer jets - not sure if windscreen or headlight washers - again, straight forward to replace. If it is headlight washers, you'll need to remove bumper to access.
I think your first bet is to identify trusted garage or mechanic and get a fully itemised quote and proceed or not on that basis. A 2015 Q3 with nearly 130k miles is probably worth less than you think, ball park retail for £7,500 trade.
Probably not what you want to hear - but that's a detailed summary.