How much would it cost to replace the master cylinder and the brake booster, and get a brake flush on a 2007 Chevrolet Tahoe?

You'll have to call them. They may be able to give you an estimate over the phone, but you'll probably be better off bringing it in. They'll give you an estimate after they look at it.

The flush should be free if you get the work done $$ the labor is money

Maybe give them a call and they will help you out. The staff was very helpful and friendly.