Through June 13, 2013, British Airways is offering tiered bonuses on the purchase of Avios, up to the maximum of 24,000 Avios per account per calendar year. The bonus tiers are as follows:
So basically if you max out this promotion you get 31,000 Avios for $685, making them ~2.2 cents per Avios.
Is that a rate at which I’d proactively buy Avios? Heck no. British Airways partners with American Express Membership Rewards, Chase Ultimate Rewards, and Starwood Preferred Guest, so their points aren’t too difficult to come by. There’s even a 35% transfer bonus from Membership Rewards through June 7.
But assuming you have none of those points currencies, there are still circumstances under which it could make sense to purchase points. Say your family of six wants to fly from Los Angeles to Monterey tomorrow (doesn’t everyone’s family?). For only 4,500 Avios per person you could get seats on American Eagle (a total of 27,000 Avios).
Meanwhile revenue tickets would cost $225 per person.
So yeah, there are circumstances where this can make sense, but they’re few and far between. And with proper planning you should have enough points currencies that convert into Avios so you’re never in a bind.