First, allow me to introduce this article. It’s an excellent dive into how much a D&D gold piece is worth in modern dollars. I recommend reading the whole thing, but for our purposes, it’s enough to know that the author’s best estimate is approximately $35 per gold piece. This is important because rather than guess the value of various goods, labor, and so on in a medieval-type D&D setting, we can make comparisons to the modern world and then determine D&D costs using this exchange rate.

The next task is to figure out which modern job is most comparable to a wizard’s. Let’s see… constantly has their noses in books, deals with highly arcane descriptions, can be totally fucked if they misspell a word or get a syllable wrong…

Easy. Lawyers.

For our purposes, it also helps that lawyers charge an hourly rate. If a wizard is running a magic item shop, they’re not getting paid a salary, so the value of the business is going to depend on how much the wizard expects to profit per hour of work.

Using the information found here, we see a rough minimum of $100/hr. for a lawyer’s service. Think of this as comparable to the value of a 1st-level wizard. That wizard may be relatively new to the magic game, but they’ve still put in a lot of work and study to get to this point, and have an expertise in the subject that average citizens can’t match. Hiring a 1st-level wizard to work by the hour, therefore, would cost about 3 gp/hr (3 x $35 = $105).

Of course, 1st-level characters can’t make magic items. The wizard has to be at least 3rd level to make common or uncommon items. If we assume the wizard’s services become more valuable as they gain experience, we can bump up their hourly rate. It’s both reasonable and easy to say the wizard is worth an extra 1 gp per hour, at least at levels 2 and 3. Thus, when the wizard is level 3 and capable of making magic items, they’ll expect 5 gp per hour, or 40 gp for a full eight-hour day of work.

Lo and behold, that’s the exact cost of one 2nd level spell. Since most uncommon items replicate effects no higher than 2nd level in power, this helps us set a baseline market cost for these items.

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Of course, there are items which should cost more than their rarity indicates. Would an adventurer spend 2,500 gp on a Bag of Holding? You’re damned right they would. 5,000 gp? Given normal loot tables, they should earn that type of scratch taking down two CR 5 lairs, so quite likely. In fact, for something as permanently useful as a Bag of Holding, a group might spend quite a bit more. 

These types of high-profit items should be more readily available in magic item shops. After all, if a Bag of Holding brings in 8-10k gp for the same 500 gp investment, why wouldn’t a spellcaster in or near a well-visited town keep one or two on hand? In fact, even a spellcaster who isn’t interested in great wealth would quite reasonably keep a handful of common item types around to serve as a method of funding their activities. If you want to offer altered or new magic items, variations on a Bag of Holding—like the Dress with Pockets—would be a very reasonable choice.

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Truthfully, that’s up to you. However, if you want a set variety of prices within a rarity of magic item, there are some extra considerations.

• 40 gp/day is the expected value of a 3rd-level spellcaster’s work. If items requiring 1st and 2nd-level magic are sold according to their lower value, fewer wizards will consider it worth the time to make them—for example, if such an item is sold for 1,500 gp, that’s 1,000 gp profit, or 50 gp per day spent crafting it. This is only clearly worth it to wizards of 4th level and below. Therefore, it’s likely the PCs will find such items for sale when they’re ready to buy them and more likely that they will have to negotiate for someone to craft it, meaning they will have to wait for it to be made. (It’s reasonable to think a wizard will take a reduced rate for a guaranteed sale, though to what extent is at DM discretion.)

• Similarly, because a wizard of 5th level or higher can make more expensive items, they’ll likely focus on those if 1st and 2nd-level-based items don’t sell for as much. Alternately, if they’re in a location with little or no competition, they may choose to make items with lower-level magic but still charge the higher amount—just because they used lower-level spell slots doesn’t make their time less valuable.

• Many items don’t have obvious connections to a particular level of spell. What magic goes into making an Immovable Rod? A +1 weapon? A Quiver of Ehlonna (or any extra-dimensional container)? Gloves of Missile Snaring? If you want variable costs within a rarity level, you have to make judgment calls along these lines. You can’t be “wrong”, per se, because it’s your campaign world and you make the rules, but it could cause unnecessary friction with players who disagree with your judgments.

• Finally, if some uncommon items can reasonably sell for 2,500 gp, there’s no good reason to offer any for less than that. A wizard who sells two 1,500 gp items makes the same profit as if they sell one 2,500 gp item, but they spent twice as long working on them. People and groups who are interested in a given item at 1,500 gp already have more money than the vast majority of the world can even conceive of; anyone selling them magic items needs to maximize profit per sale, because such sales are probably not going to come along that often. will often be able to afford it at 2,500 gp as well. Not all of them will be interested at the higher price, but the wizard doesn’t need them to be; they only have to buy half as many items at the higher price for the wizard to make the same amount of profit.

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not only won’t anybody buy one, nobody will make them for sale in the first place. More to the point, it’s hard to imagine

unless ancient mages had some secret method for speeding up the relevant alchemical processes.

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VERY IMPORTANT NOTE, REPEATED FROM LAST CHAPTER: “Available money” includes cash-equivalents such as gems and art. A merchant might pay a party with 1,500 gp, or 1,000 gp and a 500 gp diamond. Most parties treat those the exact same way—if they get straight cash and the cleric wants a 500 gp diamond available for Raise Dead, she tries to buy one, and it’s up to the DM to say if she can find one. Therefore, it is all the same for purposes of this book.