For four days only — through July 18 — is offering a bonus of 80% on purchased points.
Hilton will let you buy up to 80,000 points per year, plus bonuses. The pricing here amounts to $0.0055555 per point. I value Hilton points at $0.004, since I can pretty much always get half a cent in value at least from Hilton points and I have a preference for holding cash.