$150 is probably not bad when you factor in prep time and all. but the armor all thing??? if sand paper can't get armor-all off then i wouldn't worry about painting the mirrors, i'd just add a new coat of armor-all
i'd hope that they would remove the mirrors to paint them if at all possible, which i'd assume they can be, to avoid overspray and so forth. i'd check around and see what other shops say, you never know.