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Probably the cheapest so far. It was $20 when it was released in 2001. And it's re-released on Steam. Read the review of the Steam version here:
http://www.capsulecomputers.com.au/2014/02/moonbase-commande…
My only gripe was that it was so hard to get people interested in it as all the releases at the time were pretty much gobbling up all the mind share.
This is a really really really good strategy game for multiplayer. Extremely easy to pick up and learn.
Edit- Just read through the game description page. Looks like multiplayer is still limited to LAN. I was getting excited thinking that it might have been updated.