The maximum you should be paying for that route on a narrow body plane is around $450, and at bottoms out at about $40 (in economy). So, for there to be an upcharge of 700GBP, something seems to be amiss. I should point out the obvious, though; it's way too early to buy tickets for October travel (10/1-10/7 to/from top tourist destinations and 10/15 onwards to/from CAN/SZX are possible exceptions).