Just my observations, for what they're worth:
TC are fine on price, but if you have an issue you may as well give up - you won't get anywhere if you complain. We won't use them if we can help it - they are just above RyanAir for choice, and RyanAir are at the very bottom.
We have used Monarch scheduled where possible and have no problems. Monarch charters are different and the experience can be very different! We generally use a flight that comes in from Malaga. We keep an eye on this flight, and this is the one that causes the dely, generally, though most times we haven't been severely disrupted.
Most airlines these days use the EasyJet model where the early seats are cheapest and the last few are astronomical. The total price keeps the balance. That said, they do have peaks and troughs on this model, where certain times and days are known to incur increased interest in booking and the prices will vary according to those. Monarch, for example, have a happy hour between 12 noon and 2pm - Though I've never noticed the Dalaman flight from Luton affected by this.
I can't see cookies affecting the price - just your interest. Though if you are worried about it, following the Blue Lizard technique is probably not a bad thing.
There are some tricks - but I'll keep them to myself!!