From Exodus3000 Wiki

In Exodus3000, a player may redeem their Mars Dollars for real cash at any time when they own a Cashout Card. The amount given is determined by the exchange rate posted on the site. The cash is sent to a PayPal account or sent to the player by personal check.

[edit] How to Obtain a Cashout Card

• Found by searching Abandoned Homesteads
• 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)

[edit] Cashout Rules

• The minimum cash out is $1 USD.
• When non-subscribers cash out, all upgrades are set to zero, and all cards are removed. (Radar level will not be reduced during cash out.)
• When subscribers cash out, all upgrades are either cut in half or reduced to level 10, whichever is lower, and all cards are removed. This only applies to players who have been subscribed for greater than one month.
• Cashout cards that are found in the game may be traded in the forum. Cashout cards that are given as a bonus for purchases or subscriptions may NOT be traded.
• To request a cashout, send an email to admin@exodus3000.com

See also the official site's payout section

Exodus3000
Statistics	Weapons | Defense | Intelligence | Security | Radar
In-game Elements	Dig | Cards | Missions
In-game Locations	Mars | Homestead | Abandoned Homesteads | Settlements | Outposts | Volcanoes | Ruins | Craters | Plains | Dunes
Rules and Regulations	Alliances | Basics | Cheating | Payouts | Purchases | Special Prizes | Referrals | Cards | Dig for Treasure
Official Website	Official site