Well if you're gonna use your wife as an excuse, then you should use that "safety issue" blank check for all it's worth. If you're gonna pay that much for the diagnosis and there's a dealership around, you can get it at the dealership for that much or less and might have better diagnostic equipment, probably have better diagnostic equipment than your guy's shop and more importantly, if any of it is under factor recall, the dealership has to tell you and do the work for free.
And this is not something I would recommend and don't work for BMW and the dealership is a rip off 99% of the time but sometimes it is worth it just for the diagnosis and information on factory recall that they have in their computer database. And I'm only suggesting this cause I took my 94 530i in to the dealership for an engine diagnosis and the e-prom and thermostat are still under factory warranty in that car so all of the work was done by BMW even though it is a 94 and I am the third owner. Anyway, there's that. Get to tell them exactly what is wrong and see if you can get the parts and work done much more reasonably priced by that guy you know.
I would love to see that database, by the way.