I'm trying to book Bus tickets London - Fort Lauderdale (mid Oct) and return New York - London (mid Nov).

If I search a return on the Fort Lauderdale flights it's about £850 each way.
If I search a return on the NY flights (which are hugely expensive in Nov, upto £3000 each way?), I can find a few £1200 each way.

In the past I've done this to find the lowest priced flights on each way, and then put these into the multi-city tool to price up. Normally (ok only done it a couple of times) it prices up as each direction's one ways eg I was expecting around £2,000.

However yesterday it was coming up at £2,700. I tried to call BA and she got £3300! This morning it's saying £2,400. Very odd I think?

Is this a glitch, or is there a reason that it's adding in £500/£700 or more by making it an open jaw? Very annoying as the sale is supposed to be on too.

Any help would be much appreciated. We have to do ex-London, but £2500 for the return to and from two 'lower' priced destinations seems a huge amount to pay!

Thank you!