http://store.steampowered.com/app/311340/
Metal Gear Solid V: Ground Zeros is $10 on Steam. I'm still hesitant to jump into Metal Gear at this point since I've never played the previous games but If this price keeps dropping I may have to finally pull the trigger.
TRUST ME, you don't need to play ALL the MGS games. I lost track of the story somewhere around MGS 3.
$10 is a good price for what MGSV:GZ is, but what it is is basically a demo for Phantom Pain. Angry Joe gives a pretty good assessment of it from the perspective of someone new to the series.
The only games I'd suggest that you really need to play would be Metal Gear Solid, the original, and Metal Gear Solid 3. Solid because it's a good intro to the series and is just a really fun game in general, and 3 because it's considered to be the best in the series (and I don't see much to protest that statement.) MGS you can get on the
PSN for your PS3 for $10, which I think is a very reasonable price given how fun of a game it is, but it also wouldn't be hard to find and emulate. As far as 3 goes, well you basically have to get a metal gear collection, either the
HD collection which only has 2, 3 and Peace Walker, or the
Legacy Collection which has every MGS known to man. I say you at least try out MGS because it really is a classic. Yeah it's dated and not exactly a master stealth game, but it's one of my favorites. I've played through it multiple times and each time it's slightly different. And there's a great number of easter eggs and humorous moments as well.