The most expensive thing I ate in Penang, and indeed the most expensive thing I expect to eat on this entire trip, was this durian. Previously, I knew durian only as the fruit responsible for the rancid-sweet smell that pervades Chinese supermarkets in London. Many hotel lobbies in South East Asia have signs forbidding durian for the same reason. (I read about one of these signs and used it in Glow, thinking it was a humorous and evocative detail. I now realise that if you've spent any time in this part of the world it's as banal as 'No Smoking'.) Penang is famous for its durian farms, and in researching them I learned that a variety called the Musan King is regarded as the best of all durians – although Olexander Nechytaylo, the Ukrainian ambassador to Malaysia, recently declared, 'I don't like Musang King. My favourite is XO.' Scorning Nechytaylo and his hipster durian opinions, I decided to try the consensus pick.

I went to a shop on Dr Lim Chwee Leong Road called TNG Siang Hock Trading. There were no other customers, and the shelves were mostly empty, perhaps because it is not yet durian season. Two young assistants sat playing with their phones. However, a huge banner advertised the Musan King, and sure enough there was a display of about thirty of them at the front of the shop. One of the assistants came over and I asked him how much a Musan King was. “Fifty ringgit,” he said.

At that moment I couldn't summon the exchange rate to mind, but I knew that a bowl of noodles from a hawker stand was only four or five ringgit. Fifty was clearly an enormous sum for a piece of fruit. But how often, I thought, does one have the opportunity to try the very best of something? Never in my life, probably, will I taste the very best Iberico ham, or the very best white truffle, or the very best Japanese whisky. But this was the very best durian. Also, it had been an extremely cheap holiday up to this point. I agreed to the price.

He put the durian on the scale. At this point it dawned on me that the durian actually cost fifty ringgit per kilo. (And I wasn't being scammed – I've since confirmed that this is about the market rate when musan kings are scarce.) “A hundred and forty ringgit,” he said.

“Are there any smaller ones?” I asked. He put a different one on the scale. “A hundred and thirty-four ringgit,” he said. “OK!” I said, feeling that I'd shrewdly economised.

He hacked up the durian with a small cleaver and put it on a table for me. I sat down, pulled on a pair of the plastic gloves provided (to prevent the smell clinging to your hands), and began to eat. I should note that I'd already had a big lunch of beef rendang at a nasi padang stall. Fortunately, at 31°C with 80% humidity, it was just the kind of weather that stimulates a hearty appetite.

As advertised, the lobes of flesh inside had a remarkably smooth, melting texture, and a rich, custardy taste. However, they also had something of the durian's obnoxious bouquet. More than anything, I was reminded of the black sapote, the Mexican fruit with flesh uncannily like chocolate pudding. Black sapotes can be found in the markets of Oaxaca for as little as ten pesos (40p) per kilo, and as I ate this elite durian, I tried to work out how much it was costing me. I knew that I'd exchanged a Thai thousand-baht note at a money-changer for something in the range of 120 or 130 ringgit. I also knew it was forty-five baht to the pound, so that was... more than twenty pounds. This fruit – which, frankly, was not even as enjoyable as a ripe mango – was costing me more than twenty pounds. And I was already starting to feel pretty full.

However, I forced myself to continue eating until it at least looked superficially as if I'd got through it all. Then I counted out some notes and got up to give them to the assistant. “Take away?” he offered. Which I had not expected, but seemed reasonable, given that, at these prices, even the shreds of edible matter still clinging to the seeds were worth a little something. I shook my head. “Take away?” the assistant said again.

Why wouldn't he take no for an answer? I looked back at the durian, and realised for the first time that he'd only exposed part of the fruit with his cleaver. The other part was still intact. There was at least a tenner's worth of durian left inside. “You can give to friend,” suggested the assistant.

Why did I still refuse? Partly because, like many insecure males, once I've stated a decision in public it's almost impossible for me to bring myself to reverse it, even when I know reversing it would be in my best interests. But also I just didn't want the rest of the durian! I could imagine myself sitting there in my hotel room the next morning, gnawing grimly through the rest of this fruit for no reason other than that I'd inadvertently spent so much on it. During durian season in May and June, TNG Siang Hock Trading has an all-you-can-eat durian deal, and the thought of an endlessly replenishing supply struck me as a form of luxury torture, like being waterboarded with Napoleon brandy. I was so eager to avoid this that I felt considerable relief when I remembered the 'No Durians' sign in the lobby of my hotel, because it gave me an excuse not to take the durian back there. (But was I seriously suggesting I couldn't have smuggled it up in a plastic bag? Also, what kind of proto-fascist cur feels grateful that he's not allowed to do something because there's a regulation about it?)

But the assistant was now looking at me in disbelief. Subsequent research reveals that 134 ringgit is actually £24. (To put that figure in terms a layman would understand, it's almost 40% more than the projected RRP for the hardback edition of my forthcoming novel Madness Is Better Than Defeat.) And the minimum wage in Malaysia is 4.8 ringgit an hour. So a Malaysian working a menial job – such as these teenage assistants at the durian shop, perhaps – would have to work about 28 hours to afford this durian. And they would have to work for at least fourteen hours to afford the amount of durian I was simply going to leave behind as if it was kitchen waste. I knew that would be loathsome gesture, like some bow-tied colonialist languidly dousing his cheroot in the champagne he's decided he doesn't want any more. I tried to reassure myself that perhaps the assistant could take the leftover durian home to his family, but then it occurred to me that if there's one thing that the family of an assistant at a durian shop are definitely sick of, it's free durian. What would the maximally ethical course of action be, I wondered? Somehow sell the half-eaten durian on the streets of Penang and remit the proceeds to a mosquito-nets charity?

While I was in New York I went to two Michelin-starred restaurants with lengthy 'modernist' tasting menus – Momofuku Ko and Corton – and both times I found them less enjoyable than much cheaper meals. The amount of money I was paying for each fussy little mouthful was a calculation that weighed on me too heavily as I tried and failed to wring from it the quantity of pleasure that I felt I was owed. So what hope did I ever have of whole-heartedly appreciating this durian? Even before the economic awkwardness around the leftovers, the price was just too high.

But then, as I left, the assistant gave me 10 ringgit change back from the 140 ringgit I gave him. He'd only charged me 130 ringgit for the durian. I'd clawed back another 4 ringgit from the purchase! Enough to buy a plate of char kwey teow better than anything I ate at Corton. In fact, if I ate enough hawker food, it would be almost like I was amortising the cost of the durian across the savings I was making on my other meals. Which is what I spent the rest of my time in Penang attempting to do. But by day 4 my appetite buckled under the pressure, and I was only able to eat three meals yesterday instead of my normal six to seven. They included a serving of Kek Seng Café's famous home-made durian ice cream, which I can recommend, if you ever come to Penang, as a considerably cheaper way of finding out whether you like durian or not.