The rotors should be measured with a micrometer and this reading should be compared with the minimum published in the repair manual. Did the mechanic do this? You can't tell by looking at them. Even if the front rotors needed replacement, it is unlikely the rear ones needed replacement. The rotors can be turned for about $6.00.
Did this mechanic have a boat payment due? If he did, you paid it for him. In other words, I would say you were ripped off by price because of good parts being replaced when not required. I do my repairs myself and I haven't ripped off myself for over forty years.
I don't want to bust your bubble but the shiny rotors will be rusty in about a week or so but thats OK because rusty ones work just as good.
P E H