I don't need the extra civs and maps for now... I just want to play, so I got a boxed version from Play.com - EUR 37.99 (free shipping in EU).
It's cheap and even brings the Mediterranean map...
Every other "extra" I'll probably get later, when the "gold"/"platinum"/"extra"/"final"/whatever versions come out.
If you try to buy everything you'll just spend a lot of money on things that the Mod community will also address.
P.S. If I lived in the UK I could even get it cheaper! there's a £22.98 incl shipping!!