Move from a Do328 with 30 pax to a Q400 with 60 pax, and the various airport charges drops by about £50 per person to about £64 per head.
But that is costs per fitted seat rather than per fare paying passenger.
The answer is to find an alternative airport to LGW and for the LHR connections (particularly) it would seem that LTN might be the best alternative.
But shouldn't all this be in the NQY thread rather than the flybe thread?