Julija and I stagger stocking-footed off the party boat docked along the Quai des États-Unis and find our shoes in the bin, and, podiatrically and psychologically relieved (had I seriously thought somebody might steal a pair of Johnston & Murphy crepe-soled saddle bucks? here?) put them back on.

Hailing an unlicenced taxi — a nice car (an Audi or something) driven by a young man who claims credibly to be up from Italy, just for the weekend, to make a couple extra bucks — we got ourselves to the Billionaire Club in the Fairmont Hotel.

I’m through drinking, but Julija wants her usual. “A rum and Coke,” I request at the bar. “Fifteen euros,” I hear, and I hand across a 50 euro note. I turn and deliver the drink and turn back to get my change.

None is forthcoming.

I make a gesture of expectancy. “Yes, it was 50,” says the barman, this time with unmistakable annunciation. Too dumbstruck to respond, and knowing full well that if any woman is worth a gilded Cuba Libre it’s my irreplaceable Julija, I consciously choose the laugh option over the cry one. “Sip this one slowly, baby.”

On the plane back to London Tuesday morning I’m talking to Guillaume, a 20-something born Monegasque, in the seat next to me. “You know I paid 50 euros for a rum and Coke at the Billionaire on Friday night. I’d never seen such a thing in my life.” “Well, at Jimmy’z the cocktails are 64 euros a piece. And they’re not very good. But last year they were 78.”

And so it seems the recession has reared its ugly head even in Monaco, whose residential real estate is officially the world’s most expensive. Anyway, I’m thinking from now on in my travels maybe I’ll track a rum and Coke index…a challenge, or a counterpart, to The Economist‘s Big Mac index. Would it turn my bar tab into a business expense?