There are currently several programs offering big bonuses when buying miles and points. Two of my favorites are AAdvantage and Starwood Preferred Guest, with bonuses ending this month. If you need to top up your account balances, these promotions are worth considering:
American Airlines - up to 115,000 bonus miles
AAdvantage is currently offering a tiered bonus on purchased miles through April 13, 2017.
Purchased + Bonus Miles
6,000–9,000 + 1,500
10,000–19,000 + 3,500
20,000-29,000 + 7,500
30,000-39,000 + 15,000
40,000-54,000 + 22,500
55,000-69,000 + 30,000
70,000-84,000 + 40,000
85,000-99,000 + 50,000
100,000-124,000 + 60,000
125,000-149,000 + 75,000
150,000 + 115,000
You'll get the best value when purchasing 150,000 miles for $4,425 to achieve the 115,000 mile bonus. This brings your cost per mile to ~1.7¢.
American Airlines processes these transactions directly, so be sure to use a card that earns extra points with American to bring your effective cost per mile even lower! For example, using the American Express Platinum Card (that offers 5x Membership Rewards Points per dollar on payments made directly with Airlines), would net you up to 22,125 MR points, in addition to the AA miles you're buying.
Starwood Preferred Guest - save up to 30%
SPG is offering tiered discounts on point purchases through April 30, 2017.
Buy 5,000 - 9,500 Starpoints and save 10%
Buy 10,000 - 14,500 Starpoints and save 15%
Buy 15,000 - 19,500 Starpoints and save 20%
Buy 20,000 - 30,000 Starpoints and save 30%
If you max out this promotion, you'll get 30,000 Starpoints for $735 (about 2.45¢ per mile). Starpoints are perhaps the most valuable transferrable point currency, as they can be redeemed for hotels at SPG properties, or transferred to many airline programs at a 1:1 ratio.
Something to note: you must have an SPG account that's at least 14 days old to be eligible to buy SPG points.
The bottom line
While it usually doesn't make sense to purchase points speculatively, you may be able to get great value out of some of these bonuses if you have an immediate award redemption in mind.