ooh the title rhymes

anyways

In my campaign, I've created an ice mining town in a northern area that exports ice. They keep it cool using some magic (maybe bags of holding? I think a closed bag of holding filled to the brink with ice would probably be unable to warm up) and sell it for usage in keeping food fresh, as a luxury commodity, and some other reasons. Ice is in very high demand (for some reason) and they are the only large and consistent supply of it. How much would they sell, say, a pound of ice for? How would that work?

While, pre-refrigeration, mining ice and shipping it elsewhere was actually a real business (no magic required; you just take huge blocks of ice and wrap them in some sort of insulation, such as straw), the price was pretty much entirely determined by transport costs and would be more per ton than per pound. You're probably going to want to explain how someone isn't using magically created ice (shape water is fastest, but you should be able to create ice in decent bulk with any cold damage spell or cantrip) to undercut their business.

https://en.wikipedia.org/wiki/Ice_trade

Magic isn't common (though not particularly rare, either), and shape water ice is temporary. Cold damage spells at cantrip level don't make any long lasting ice, and at any later level you're wasting magical resources that you may want or need. Either way, consistently creating ice at a large scale would be a very difficult, unrealistic, and not lucrative trade for a spellcaster.

Quote from 2014_better_than_2024 >>

Magic isn't common (though not particularly rare, either), and shape water ice is temporary. Cold damage spells at cantrip level don't make any long lasting ice, and at any later level you're wasting magical resources that you may want or need. Either way, consistently creating ice at a large scale would be a very difficult, unrealistic, and not lucrative trade for a spellcaster.

For an elf or low level spellcaster who doesn't have much magic, setting up an ice stand and using shape water would be fairly lucrative. It's almost no work, and the materials are practically free.

In cases like this, I think you just have to go with your gut. D&D doesn’t do economics — no matter where you go in the multiverse, a longsword is 15 gp, regardless of how easy or hard it is to get iron, or how many smiths you have with shops adjacent to each other, etc. it’s the same price.
So I’d just look through the mundane equipment list, and pick a price based on something you find comparable in value, and just go with that. Unless the variety in the price is really plot critical, I generally wouldn’t worry about distance and such, just keep it simple — costs the same everywhere.

And if we’re brainstorming reasons why people want it instead of shape water, or just cooling things with prestidigitation or other magic:

It’s laced with ancient magic so it stays ice for unnaturally long periods, and when it melts, the water acts like a potion of healing.

The ice goddess blessed the glacier it’s taken from.

Neither of the above is true, but people think it is. In reality it’s just plain ice with a good marketing scheme.

It’s nothing special, but the royals just have to have real, artisanal ice at their weddings. So now anyone who’s anyone has to have it. And so do the people trying to climb the ladder into a higher social class.

We have a bag of holding in one of our parties that chills everything in it to ~35F/2C. In another they have a haversack and one of the smaller pockets keeps things cold.

Now I'm picturing a Bartender that can cast the Frostbite Cantrip, and chills glasses of Ale as he hands them to patrons... lol

I think the Critical Role team had an item like that. I forget if it was campaign 1 or campaign 2. They called it the, "Bag of Colding".