You're right, it isn't particularly realistic, I'll change it to him having a knife on hand instead and then having the drawer he's going for have some kind of firearm in it.
As to the currency, maybe just some some system like the one Star Wars has, where I think we're supposed to assume that each credit is worth roughly one U.S. dollar (don't ask me how I came up with this. It's just an arbitrary conclusion). I had an idea that all money was digitized and controlled by banks, and while that gives some interesting potential for plots it would over-complicate the pirates' raiding to a point where I don't think its worth the trouble.
In other words: I don't really have any idea that would work, other than using some system that is roughly analogous to our money system, and really we just need to know enough about it for the reader to know when amounts of money are big and when they aren't.
What a piece of work is a man! How noble in reason, how infinite in faculty, in form and moving how express and admirable, in action how like an angel, in apprehension how like a god -- the beauty of the world, the paragon of animals! — William Shakespeare