Dennis: I think we made every single one of our Paddy's Dollars back, buddy.

Mac: You're damn right. Thus creating the self-sustaining economy we've been looking for.

Dennis: That's right.

Mac: How much fresh cash did we make?

Dennis: Fresh cash! Uh, well, zero. Zero if you're talking about U.S. currency. People didn't really seem interested in spending any of that.

Mac: That's okay. So, uh, when they run out of the booze, they'll come back in and they'll have to buy more Paddy's Dollars. Keepin' it moving.

Dennis: Right. That is assuming, of course, that they will come back here and drink.

Mac: They will! They will because we'll re-distribute these to the Shanties. Thus ensuring them coming back in, keeping the money moving.

Dennis: Well, no, but if we just re-distribute these, people will continue to drink for free.

Mac: Okay...

Dennis: How does this work, Mac?

Mac: The money keeps moving in a circle.

Dennis: But we don't have any money. All we have is this. ... How does this work, dude!?

Mac: I don't know. I thought you knew.

Great scene

You forgot the best line: "I don't know how the US economy works, much less some kind of self-sustaining one".