Disagree with £1-2m.
A lot depends on how you allocate overheads. Eg a DFO. Can be a pilot so are you allocating him as a pilot or just a DFO? A lot of post holders can fulfil a role which would need staff anyway without allocating it to the AOC column.
Maintenance control is contracted out with only a few aircraft.
I performed this exercise for a Premier some time ago. Seem to remember set up was in the 100k band. With annual costs around 60k. This included Part M. Obviously fees for an ATR will be a lot more but even still 1-2m could be a bit extreme.