I believe the Groupon offer came out cheaper than that, but no real way of knowing if that will ever come back again.

Rather than just buy Avios, I invite the OP to look at ex-EU options. A return PE --> J upgrade to NYC costs 48,000 Avios off-peak and 40,000 Avios peak. Let's say £500 to buy those Avios at a bare minimum. Plus the underlying PE ticket of course.

You can easily just buy the J ticket for £1,000 or less just by positioning to Dublin or Oslo. And without having to mess around with award availability. Anyhow, just a thought... it's so rare to see people wanting to buy lots of Avios because there are often better ways of doing things.