Originally Posted by DYKWIA

I assume your are looking to book flights in Economy?

No sure if this a goer, but how about using your Avios for the accommodation rather than the flight? Then pay cash for a Virgin, United or Thomas Cook (there may be others) direct flight.

Using Avios for economy flights is generally very poor value. As you have seen, it's often cheaper to buy a cash flight rather than pay the taxes.

Originally Posted by cameramaker

It depends on your budget, but a return from MAN-JFK in W can be quite competitive, often cheaper than from LHR. You could then use your avios to upgrade to Club World. Or a Y flight out to JFK and then a W return, again, upgrading your inbound to Club World.

Alternatively, if you want the absolute lowest cost option, your avios could book you some really decent accommodation in Manhattan. While you wouldn't be realising the best value/avios, its a way to certainly bring the cost of the trip right down.