MY PEOPLE!
*ANGELIC CHORUS*
I descend from the heavens to bring you news of a fabulous deal. Brave New World (Civ5 DLC) is on sale right now at Gamefly.
Now this totally works on PC, however, it is listed as a MAC only code. It is tried and tested by yours truly. PC has been given a different price, ignore it.
Shop for the MAC version of BNW. In the UK it is £5. There is a 25% reduction code available, reducing that to £3. UK Code: GFDJAN25UK
Normal price is £19.99!
People in the US, I am sure you can find a similar code. They often prompt you to enter your email address and supply you with such a code if you sit on any given Gamefly page long enough. A few minutes at most.
Hope that all makes sense. I have tested this myself. You simply take the 15 digit code and place it in Steam, as you would normally. Here are some "testimonials" that will indicate the same thing:
http://www.hotukdeals.com/deals/28th-january-only-brave-new-world-3-95-with-code-steam-gamefly-1807132
http://www.amazon.co.uk/Meiers-Civilization-Brave-World-Online/dp/B00E1OB53C
There you have it. I'm pretty sure, if you have the base game, the MAC version is completely compatible with Windows. I have launched it and it works fine.
Suck it, Dealzon! (I love you, Dealzon)