If you can get hold of CTP for $5 then that is the cheapest option. Go visit the CTP forums - i know alot of PBEM goes on, and there may some LAN players around to give you advice.Check to see what downloads/mods you can use.
As for CTP2, i've had fun with it in LAN MP and if you can get cheap copies and dont mind a few rough edges i'd definatly recommend it.
Those are the cheapest options i guess, as Civ3 PTW is still a full price release. As for Civ3 i've never played it so can't comment.
Good luck and hope you find a game to enjoy in MP
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'The very basis of the liberal idea – the belief of individual freedom is what causes the chaos' - William Kristol, son of the founder of neo-conservitivism, talking about neo-con ideology and its agenda for you.
info here. prove me wrong.
Bush's Republican=Neo-con for all intent and purpose. be afraid.