All info regarding cashout can be found
http://exodus3000.wikia.com/wiki/Payoutsrate of cashout payment depends on your ingame stats.
if you have built up your weapons/defence/security/intel. you will receive a greater exchange rate to $USD for your Mars$ than if you have done no/few improvements.
Cards are gained:
* Given out to subscribers after having been subscribed for a total of three months (beginning October 1st, 2007)
* Given out to players who spend a total of $75 in the game during any time period (beginning October 1st, 2007)
* Dig (The Dig feature allows the player to "Dig for Treasure" once, every day, after all the player's daily and anytime moves have been used up. The reward prize the player can get for 'digging' is determined randomly.)
* Through Mission "Get your butt off Mars".