That is about right for a price range, because the bulk of your cost is labor. Realize that the head gasket is under $30 depending on which kind you get. Speciality shops could cost more, or less if the are giving you a deal "because you are one of them", Chain garages are usually on the higher end. and Mom and Pop shop could be cheap 'cause they need business and the mechanics might not be ASE cert'd.
I would stay away from the cheap shop on this one, $200 at minimum and make sure to get a warranty on the work. Too many bad things can happen when the engine gets opened up.