Learn Dutch: Die besloten club kost niets anders dan een enorm vermogen. - That private club costs nothing but a huge fortune.

Literally, it translates to "nothing else than." Just like in English, it is used to emphasize that there are absolutely no other requirements or outcomes. In this sentence, it acts as a fixed phrase introducing the noun een enorm vermogen to stress the sheer exclusivity of the cost.

I learned that besloten means "decided." Why does it mean "private" in besloten club?

While besloten is the past participle of besluiten (to decide), the verb originally also means "to close off." In the context of a group, event, or venue, a besloten club is a "closed" club. It means it is restricted, exclusive, or private, and not open to the general public.

Doesn't vermogen usually refer to "power" or "ability"?

It does! You will often see it used for mental or physical ability, or engine power. However, in financial contexts, vermogen refers to "wealth," "assets," or a "fortune." Here, een enorm vermogen means a staggering amount of money.

Since this is a comparison, is it ever correct to say niets anders als?