Well, for starters: Don't buy the 'cradle'-maps. They're not really worth it, I think. And there isn't a 'combo-pack' out yet for all DLC-civs. But once in a while, as is common practice with Steam, there's a sale on. A few weeks ago everything was 40% off. And I bet during the summer sales in june (Steam as two big sale periods, summer and christmas) the Civ 5-sale will be there again. Then you can get all DLC-civs at a discount (so far, if it's again 40% off, that would be about a bit more than 9 euro's, in dollars around 13½ dollars).