I may be being simplistic here but, having flown the F27 and the Airbus family, we are talking apples and pears.
Savings on DOCs for an F27 cannot involve changing the basics of the thing - far, far too expensive to develop. Anyway, which F27 are we talking about; a basic one or a curly-prop one?
You are down to crew costs (first option), airfield fees, fuel price and engineering costs. OK, you can mix these up with FOCs a bit but we're talking costs here.
Will the local authority permit only one cabin-crew? I am assuming you have about 44 seats.
What is the local equivalent of Eurocharges (ATC fees)? Any room there?
It never ends...