Assume you mean '05 987, correct?
Regardless, $900 is very steep. Figure dealer o&f should be $250-300 at most and brake flush $200-250 at most. Now, if they did a major maintenance like those above plus check polyrib, change plugs, change cabin and air filter, then $900 seems to be the going rate. But for just brakes and o&f, that's almost double what it should be
