At the top end, 20,000 points will cost you $560. These can be converted in 25,000 airline miles in the majority of programmes. The price per mile works out at 1.4p, which is certainly not a bargain but less than a lot of airlines charge for buying their miles directly.
The rules are straightforward – points post within 24 hours, maximum purchase of 20,000 points per year, your SPG account must be 14 days old to participate.
The ‘sweet spot’ with Starwood is their cash and points awards for mid-tier properties – eg the Sheraton at Frankfurt Airport (good for anyone on a Lufthansa award flight ex-UK) on November 13th is Euro 239 or $60 + 4,000 Starpoints. Even if you had to buy all the points from scratch via this promotion, you would still save a whopping £86 by buying and redeeming points.