There are two discounts that could be available depending on your status, though it still won't be cheap.
AARP offers $200 off BA business class when booked on their site.
Then I've had some luck applying the 10% discount code for Chase's BA cards to the AARP rate for other Chase cards. It's CHASEBA10 but it gets a bit tricky. It seems some days the discount works on the site. Other days on the exact same flights it doesn't