OK; understood. Do you have any points anywhere that are convertable to airline miles (e.g., Starwood Preferred Guest points, Amex Membership Rewards points, Chase Ultimate Rewards points)? A PIT-LGA one-way on AA in November is currently available for just 7,500 AA miles, or 7,500 BA Avios. If your current job requires travel that involves frequent hotel stays/car rentals, that is another easy way to amass FFP miles.

If you must pay cash, then I would look at a PIT-NYC one-way (unless DL suddenly drops the mileage needed for that flight to under 10,000 miles -- stranger things have happened); and then price an open-jaw ticket NYC-LON-PIT, using the "multi-city" booking engine at various online sites, including the airline sites, as well as online travel agents.