You can replace the Mass Air Flow Sensor yourself. It's 2 screws and a plug, and on top of the engine. 1st you can get some Mass Air Flow sensor cleaner from Autozone etc, remove it and spray it. Sometimes this works just fine. If not, check eBay or www.oembimmerparts.com or getBMWparts.com < (wholesale BMW parts)

As far as the laundry list the dealer gave you, it's a joke. Dealerships are there to make money, and they love replacing everything in sight at your cost.

Some things on the list will need to be replaced, but do it at your own discretion. If the washer tank is leaking, seek out BMW parts recyclers and save yourself a ton of money. Being that it's a 10 year old vehicle, there are many great parts that you can find out there. Of course when it comes to typical things like power steering lines, go new and go OEM. But do use a board sponsor or one of the above to get the best pricing.

I went to BMW once 6 years ago for an oil change. The charged me about $200, I never went back. Filter $10 Oil $60-$70 Labor at most shops if you supply the above is never more than $15-$20 bucks.

Good Luck with the X5. Try not to stress too much about it.

Electrical - Powertrain control - Mass air flow sensor mass air flow sensor, x5, 4.4l
00-03
$337.46
This is from getBMWparts.com - in essence your dealer is charging $363 dollars to remove two screws and replace two screws.

If you want to spend even less for OEM BOSCH

X5 Engine Mechanical & Under Hood Parts
$174

I would pay the diagnostic labor fee and take it elsewhere STAT.