As pointed out, vaulted ceilings cost more . . . . infact, it less money to go to 9 or 10 ft flat ceilings then some vaults. Or consider a Tray ceiling  ..  . . as the word suggest, the ceiling is shaped like a serving tray. Starts out at say 8ft and tapers upward to a 10ft ceiling. Less money then vaults and can get all utilities and such run. Also allows less problems with insulation