Buy Garry's mod 10 off of steam.
Garry's Mod 10
There is, 10$ Steam
technically yes, there were a few updates it is still called Garrys mod 10 though
gmod is 10$ at garrysmod.com
10 is better, $10 Steam
yes
Off of Steam (10$) (http://store.steampowered.com/)
You can get Garry's Mod 9 for free, yes. But Garry's Mod 10, (11), you have to pay for. But Garry's Mod 10 is really worth it, in my opinion.
gmod 9, yes gmod 10-no
go to steampowered.com make an account download steam on your computer and then go to the the search bar and type garrys mod and download it it cost $10 you have to have a game source though like half life the cheapest source is half life death match
Install steam (steampowered.com) and you can buy it on there. $10 and you get automatic updates through steam and servers.