Hilton have regular promotional offers for the purchase of Hilton HHonors points. The current promotion is for a 25% discount on the price of Hilton HHonors points. The promotion is valid through to 15 July, 2015.
Hilton HHonors normally sells the points at 1 (US) cent per point. Under the current offer, that will give a price for the points of 0.75 cents each.
Hilton HHonors has an annual purchase limit of 80,000 points.
Hilton HHonors recently had a promotion offering a 100% bonus on the number of points purchased, which is effectively a 50% discount on the purchase price. This offer is somewhat less generous, so may really only be of use if there is some immediate need for the points.
The Hilton HHonors purchase page may be found at this link.