How do you unlock a character in resident evil 5 mercenaries?

To unlock characters in Mercenaries you have to get over 40,000 in single or

over 80,000 in duo.

For the actual game, you can only unlock more costumes.

For 1 costume for Chris and Sheva you have to beat the game then

purchase (for free) at the bonus section. You can also unlock 2 more

costumes when you get 25 and 30 emblems.