About 15 years ago, when both of my sons were 4 & 9 years old, we rented a car in FL. My older son was goofing around in the back seat, chucked his flipflop over the front seat, hit the rearview mirror (a high end, fancy-dancy thing glued directly to the windshield--it may have even had some type of connection to the electric system), knocking it off of the windshield and breaking the mirror & mounting. I was livid, but really worried about the rental costs because we had no coverage.

Needless to say, we high tailed it to the nearest car dealer service department, ordered a mirror, and had it installed 2 days before we returned the car. If I recall correctly, we "went on the cheap" and although the mirror was replaced, I don't think it was quite the primo one that had been in the car. The cost differential was $40 vs. $200......
Happily, no one ever noticed the switcheroo!

I'd have done the very same thing in your shoes. You saved yourself a lot of $ and headaches!