Believe it or not, but even in Japan, vending machine prices are 2-3x what you’ll pay in a supermarket. You just don’t notice it as much because prices are low in general.

A supermarket can coffee will cost maybe 60-100円 for what you pay 120-200円 in a vending machine.

I didn't find that to be true to such a degree.

I was tracking the prices of vending machines pretty closely in Japan, and if you didn't jump at the first one you saw and waited until a more out of the way one, you could typically find almost anything in the 100-120 yen range. My favorites were the "100 yen special" machines where most or all items were 100 yen. The prices were in large red lettering to emphasize the deal. Prices could go up to 160 yen or higher in the vending machines in tourist areas, especially the ones inside ticketed attractions.

100-120 yen was around the price you'd pay for those same drinks in a convenience or grocery store, with the only exception being bottled water. You can find bottled water much more cheaply in the grocery stores than anywhere else, well under half the price by volume. This is a pretty universal rule of travel that I've found holds true everywhere.

Those 100 yen machines are rare. I lived in Kyoto, and can recall seeing only one in the city. People would go out of their way to use it. More typically, you will see machines that have 120円 prices by reducing sizes. Buy the same drink in the conbini next door, and you’d get twice the volume.

Regardless, if you’re in a place where vending machine prices are lower than usual, it only means that the store prices are lower still. There’s no magic here; the vending machine operators are making a healthy profit.

For what it's worth I saw more of them in Kyoto than in Tokyo. I was staying around here: https://www.google.com/maps/@35.0086507,135.7541648,17.51z

It did bother me that I could never tell what the actual size of the drink was going to be. Is it in kanji, or is it just not listed at all? I definitely had a situation where I was expecting a full normal sized bottle of green tea but got a smaller one.

Same here. I never buy from vending machines in the US or Europe. In Japan, the prices are low and the quality good, so I bought several things, including ice cream. There's no way I'd buy the garbage ice cream we make in America from a vending machine, but the stuff in Japan is pretty good and a nice treat on a hot day, and was only Y140.

Slightly OT, but I haven't heard this: are the vending machines in Japan dispensing real ice cream and not soft-serve? Very interesting, if so I would imagine the mechanics have to be far more robust/complicated. Or is it still soft-serve, but just higher-quality?

edit: by soft-serve, I mean any of the thinner ice cream/frozen yogurt alternatives as opposed to the (usually very thick) real ice cream.

No, the machines I got ice cream from were dispensing real, solid ice cream. They were shaped as cones and on sticks for easy handling, but they were real ice cream, not that soft-serve crap.

Yes, I imagine these machines would have to be pretty robust to maintain those temperatures in Japan's hot climate.

Note: some varieties actually had waffle cones; others did not. There were also handy recycling bins right next to the ice cream machines, placed by the vendor, just for the rubbish from that machine.

It affects my behaviour as a consumer. In Europe I tend to purchase snacks and lunch in supermarkets or convenience stores at the bigger stations before travelling (but rarely those on the platforms because of the prices). In Japan, I just get it from any convenience store (including those inside the gates) or the vending machines without a second thought.