Fighting for the good reason is the only reason to fight. Money is just a frivolous need that everybody gives a lot of importance to. Some things are just bigger than money or anything artificial in this world. Helping someone in need, especially when it's a girl / woman who wants to save her country is the best thing to do.

Besides, they're a bunch of old guys. Gonna die in a few years anyway. :P (Joke)

A team of elite, highly-trained mercenaries known as The Expendables are sent into South America to overthrow a ruthless cold-blooded dictator. But once the mission begins, they discover a plot far more sinister than they were led to believe. With innocent lives in the balance, The Expendables are forced to take on an even more difficult challenge.