What dates? most airlines have not released prices yet for August.
Prices tend to be high on realease as they know many people are waiting and want to book. Usually better waiting for an offer but no-one can know the best time to book.
You need to be as flexible as possible, with dates, UK airports & US airports. If you are only willing to fly direct you will often pay a lot more. I have just booked Easter, VA direct £1215, Delta indirect £477.
Good luck.