Montenegro has around 626,000 inhabitants - smaller in population than many European cities. But its entry into the European Union opens a question far larger than its size: who will pay the bill for the next enlargement? And the answer to that question concerns us directly too.

The European Commission estimated that admitting Montenegro would cost around 3.2 billion euros. Spread across Europe's taxpayers, that's less than one euro a year per person - or, as they put it vividly in Brussels, less than the price of a coffee. So the sum isn't the problem. The problem is the rule that will be set - because the way Montenegro's membership gets financed will become the model for everyone who comes after it. Macedonia included.

Redistribution or new money?

The main dilemma in Brussels is whether the money for new members will come from redistributing the existing budget, or from new revenue and higher contributions from states. Germany, the Netherlands and the other net payers will probably insist on redistribution - so as not to pay more. The southern and eastern members fear that means less money for agriculture and regional development. The northern ones want the budget steered toward defence and competitiveness. Everyone is pulling the blanket their own way.

Montenegro is currently the most advanced candidate country - it has opened all 33 negotiating chapters, 18 of them provisionally closed, among them the latest on competition and the customs union. The ambition is membership in 2028. That makes Podgorica the first real test of what the new wave of enlargement will look like - not just politically, but financially.

And here's the Balkan point. Macedonia has been waiting at the EU's door for years, and the debate over Montenegro is in fact writing the price list for all of us standing in the queue behind it. If the solution for Montenegro turns out to be "through redistribution, no new money," then every next member - us included - enters a club where the existing ones already get less each, and don't greet the new guests with joy. Enlargement doesn't get stuck only on reforms and chapters. It gets stuck on one unpopular question nobody wants to ask out loud: how much it costs not to let you inside.