That works out well. I decided on 500 gp at the moment based on what little I could find. That allows the buyer to re-sell for a profit.
Sounds good.
So, I remember the time before the internet. Take something as commodity as MtG cards.
The value of a card would vary from place to place. Eventually someone started publishing a magazine with "standard prices". It was also naughty word.
There was no functioning global market in cards, so there was no global price.
In 5e, that is presumed also to be the case. Not only that, but magic items aren't supposed to be so common that there is a standard price for them even locally.
Regardless of the intentions in 5e, there's no way something like that wouldn't be bought and sold, so guidelines would really be helpful. It actually gives the group just enough to buy passage to somewhere they need to get to, so it works out well.
There are! Items have rarities, and those rarities have large price ranges.
Those price ranges should not be taken seriously.
I mean, even a +1 vs +2 sword. Suppose you are in-world. What tools can you use to distinguish between them? One of them is sharper and stronger and easier to swing, but that is very qualitative.
The +1 sword with a fancier pedigree and more impressive runes could easily be considered the "more powerful" sword and be "worth" more to some buyer.
I'm sure there might be a school of enchantment in some corner of the world that develops an objective measurement system, but that is going to be exactly one place, done by a few magical nerds, and being nerds there is going to be 7 competing systems developed by 4 different people who all think the others are fundamentally wrong.
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If they want to sell the wand of sleep, it is a small adventure hook. Finding a buyer, making sure they aren't being cheated, maybe even the form of payment.
Like, someone finds a noble with insomnia who is willing to pay for it, but is low on liquid assets; they are willing to sell you a herd of cows for it, including an prize winning bull.
That herd of cows and the bull is worth decent money, but only if delivered to a nearby city.
And so it goes.