Steam is putting all Metal Gear Solid titles on sale.
Get Metal Gear Solid 5: The Phantom Pain for $28, other MGS games cheap in Steam sale
The entire Metal Gear Solid series, well, the ones available on Steam at any rate, is currently on sale. That includes only the games, but not multiplayer DLC or single-player cosmetic items, unfortunately.
All deals are live now until 10am Pacific/ 5pm GMT on Monday, May 30. You can see the full list at the link.