Best deal I found was from direct-travel.co.uk.
Can't remember exactly how much but cost me somewhere about 80 or 90 pounds for annual worldwide travel cover to include flying, which was much better than most other quotes I got. Lots of places just don't cover flying at all, and most others started with the standard quote then added a daily premium for each day you intended to fly, which for anything over about a week added up to a lot.
I think the single trip option didn't work out at much less which was mainly why I went for annual cover.
You can only get a quote to cover flying (and other hazardous sports, activities etc) over the phone though and not on the website. The phone number is on the website. Good luck!