I'm not really sure why you wouldn't be comfortable in a "cheap" tuxedo. The Joseph A. Bank and Suit Supply (assuming you close the vents) are both cheap and sartorially correct. There is no reason to feel uncomfortable in either. You would just want to get a few alterations done to make sure they fit, and you should be good.
Yes there is. He'll feel put upon and thus uncomfortable. To me this would be like wearing a uniform simply because you have to. There are times and places for that, but this is presumably a social occasion.
Wear the midnight blue suit. If you stay with this woman and such events are part of her regular life, then invest in a proper dinner suit.