Civ V is a great game, but yes, you will shell out a lot of $ if you want to get the 'Gold Edition' with all of the expansions and DLC.
You will shell out a bit of money, but the gold edition is 50% off on steam atm, along with the expansion brave new world. It would be around $40 to get them both while on sale. Keep in mind that they might go on sale for more tomorrow or the next day since they are having autumn sales until the 3rd. Gold edition contains the following:
Sid Meier's Civilization® V, Sid Meier’s Civilization® V: Babylon (Nebuchadnezzar II), Civilization V: Cradle of Civilization - Mediterranean, Civilization V: Cradle of Civilization - Asia, Civilization V: Cradle of Civilization - Americas, Civilization V: Cradle of Civilization - Mesopotamia, Double Civilization and Scenario Pack: Spain and Inca , Civilization and Scenario Pack: Polynesia, Civilization and Scenario Pack: Denmark - The Vikings, Civilization V: Explorer’s Map Pack, Civilization V - Civilization and Scenario Pack: Korea, Civilization V - Wonders of the Ancient World Scenario Pack, Sid Meier's Civilization V - Gods and Kings.
I believe the only important thing missing is Brave New World. As mentioned earlier Gold is $25 and BNW is $15.