Through September 16 Hilton HHonors is running a sale on Hilton points. You have to log in to see the offer, so it’s possible some people don’t get the full 50% off, but I haven’t heard from folks yet that are offered something else.
Hilton usually charges a penny apiece for points, so with this bonus is selling points for half a cent each. That’s tied for the cheapest I’ve ever seen (in June 2015 they offered a 100% bonus on purchased points).