A lot of your problems could have been avoided. And most of the time things on a vehicle fail due to the owner: how they drive and what conditions they drive under.
Your mechanic is overcharging you by a mile for starters. Find a new one.
Complaining about having to replace your brakes "again" after 40k miles does not give you the right to complain about GM breaking your budget. The A/C compressor seizing could have been prevented, had you serviced it. But I didn't see you mention that on your list of expenses.
There is oil that is injected inside the compressor, before/with the freon, that prevents it from going bad. Just because it still gets cold, doesn't mean it doesn't need serviced.
And also you didn't say your mechanic diagnosed the coolant system that "continues to leak", so I take it you diagnosed it yourself. And you bought stop leak for your radiator, thinking that would solve your problem. And it didn't.. WHY? Because that stuff is made for aluminum, not rubber hoses, which by the way cost the same as STOP LEAK. And a rubber hose can't be blamed on GM; Maybe that mechanic of yours can be blamed for not putting things together right and letting that rubber hose rest on something that gets hot, which in turn can wear a small hole. Hell, even the vibration from pot holes and bumps can wear out rubber if it's resting on anything.
Again, with your airbag scenario... Check out this report by Consumer Affairs : (Knowledge is Power) http://www.consumeraffairs.com/automotive/gm_airbags.html. You will find in the very first lines by this reliable source that EVEN your "RELIABLE IMPORTS" HAVE AIRBAG ISSUES! Not just GM. This entire thing may sound like I'm being mean to you, but it's not my intention. I will have to admit though I am aggravated that you ASSUME that it's the manufacturer that's to blame. Most problems, like I said, originate from the operator. And ASSUMING that import is better. Nothing's made to last forever. But you should know, that study after study in a five year period OF ALL THE CARS OUT THERE, that GM still beats your "reliable import" out of the water by a long shot. When you spend less, you really do get less. I can't blame you though, you don't seem to know much about cars. Hopefully this might change the way you look at things. I wouldn't be wasting my time if I wasn't a mechanic for the last 25 years.