Amsterdam is actually quite expensive. And hotels are not cheap. Why not go to Berlin? Lots of LCC flights there. It's still pretty inexpensive, particularly for alcohol. It's open all night, including public transport. And while it has a massive amount of tourists now, its sidewalks are much wider than Prague's (which would be my other recommendation for partying cheaply), so it's easier to maneuver around. And they're on the Euro.