As you kill enemies, destroy containers, search pillars, etc., bounty may appear (the currency in the game).
The best source of bounty is attained by selling items/blueprints that you pick up (and don't need). You can sell these items/blueprints by going into the equipment menu and pressing "the back button". Then, highlight the item you want to sell and press "the Y button".
*Note: you do not need to have one-million bounty in your possession at the same time, so do not worry about spending your bounty.
(FYI-I used the too human 360 achievement guide Credit for this solution goes to Hayden)
http://www.xbox360achievements.org/forum/showthread.php?t=88...