A jet going 4k nm will spend around 10 hours in the air, one way. This does not count the fuel cost of 2 take-offs (which this simulation DOES take into consideration). You are running older 737's, and I am assuming you are not wanting to get any of the new generation (which could do the flight non-stop). So, let's make it a '37-5, burning 2,490 kg per hour.
24k kg per hour per flight (not counting take-off or landing) at 689 per thousand kg of fuel is $16.5k in fuel alone, which will amount to over $80 per seat. The price "last" May was 20% higher. At that range, you are not getting much more flying in, so you will need to account for the full cost of the lease in that one flight a day.
It *is* doable, and it will give you routes that will likely not have competition (and great bragging rights), you just need to have enough more reliable fuel sipping birds (your ATR's work GREAT for that) to cushion the blow of a fuel spike.