I can't tell if you have to buy anything to play GoldenEye: Source. Is it free? Are there any good tutorials on getting this up and running?
Yes here is the link to the current download version if you already own HL-2
GoldenEye: Source Beta 4 is the first major release since Beta 3.1.4 in March of 2009. Beta 4 brings us many steps closer to a final version of the mod and introduces a tremendous amount of polish in both gameplay, coding, and presentation. Some of the major changes include Rolling Explosions, Bullet Penetration, and Living Daylights, Capture the Key, and Live and Let Die gameplay scenarios. Please see the Beta 4 Change List for a complete list of changes in Beta 4.
Their wiki is a good source for tutorials