In what seems to be a reoccurring promotion over the past few months, United is offering up to a 40% discount on the purchase of MileagePlus miles through October 31, 2012. You must use the links on this page in order to qualify for the discount.
They’re offering a 20% discount on the purchase of up to 30,000 MileagePlus miles, and a discount of 40% on the purchase of 30,000 or more MileagePlus miles.
With this promotion between 30,000 and 100,000 United MileagePlus miles can be purchased per account for 2.1 cents each, plus a 7.5% excise tax, for a grand total of ~2.25 cents per mile.
This isn’t “steal,” though this is about as cheap as United miles get. United miles are among the most valuable mileage currencies out there, so if you need to top off an account (with 30,000+ miles), this is a great promotion through which you can do so. If you’re going to buy fewer than 30,000 miles and have a card that accrues Ultimate Rewards points, you’re better off purchasing Ultimate Rewards points and transferring them to United.