I assume that all the things you mentioned went out at the same time and if so that would point to a common point of failure in my book. While the dealer knows more about the car than I do, I don't think that the master lock module has any control on the switch for the dome light and possibly the door locks. I could see it controlling the window and mirror though. To see if this is a ground problem you could try running a test jumper between the chassis and a good ground point on the door though I have my doubts that will help in this case. I suspect a power problem is the cause but I have been wrong before and may be again.
The 250 dollar switch that one dealer talked about could be the problem if it ties to all the things you mentioned. I would guess the switch contacts could be cleaned if that is the case. You should be able to get some data from alldata.com I would think and the info would be well worth the purchase cost to help find the source of the trouble. If you are going to keep the car for some time I highly recommend you purchase a factory service manual for it along with a test light probe and a DVM meter, if you want to work on things like this yourself. These things will save you a lot of money in repair costs and time an can pay for themselves in just the first repair.