Cost for a rear differential gear swap?

Hello, very simply I have a 2012 Ford Mustang V6 with the stock 2.73 gears and I ordered 3.73 gears and I wish to have them installed. My local auto body shop is asking $1000 for the installation + gear oil + engine retune (apparently that s needed when you jump gears like that). Is that a fair price or should I look elsewhere?

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