What is included?

I'm looking into buying Civ V w/ the G&K expansion pack, but I just to clarify, if I buy just the G&K expansion pack, does it also need the vanilla version to run and thus I would just waste my money? Does the G&K expansion pack include the vanilla version to begin with, or is it just G&K?

Or do I need to buy the gold edition to get both vanilla and G&K in one package?

I was going to say that G&K doesn't run without vanilla Civ V but upon further inspection G&K doesn't have the same DLC tag that Brave New World and the various civ packs do. Strange.

It's an expansion and needs the base game. You can buy the Gold Edition for like $50 on Steam. Buying Vanilla, then G&K, then all the DLC's will be like $120