That's an eye opener, I am thinking of picking up a used FF Sony and need to factor that in. Just had the LCD replaced on my out of warranty D700, which from the service manual (yes, I entertained the notion of opening it up) requires a very serious amount of disassembly. Nikon in El Segundo quoted me 224.00 and held to it, I had it back in a week and am glad to see this wasn't a blanket flat rate job.
I'm guessing you've already contemplated sending it to Precision or another well regarded repair shop?
DeOxit liquid is said to work minor miracles with some unexplained errors. If you haven't already, find some and treat the lens mount/contacts/battery grip contacts, everything you can find before sending it in. The A900 may also have a factory reset sequence and that's worth a shot as well. Do keep us updated.