The recommendation above to look through the Tier Point runs thread is a sound one. A tier point run should bag you the most TP per pound (dollar, euro) spent. For example, my trips last year averaged £2.57 per TP. Some people get much better deals than that but I consider around the £2.50 mark to be one I'm willing to pay.

The better deals often start outside of the UK because either the airline offers a lower fare (or lower surcharge, often called YQ) or because you're avoiding UK APD. However, you need to balance that with the need to find your way to the trip starting point and potentially the cost of an overnight stay.

It's a deep rabbit hole to disappear down, be careful!