If you really NEED to put specific prices on goods or services in your story, it may help for you to draw up a list of ALL the prices for things your characters may need or want to buy, so you can slot your fictional items into the schema wherever they make sense within the economy/culture of your story. Note that the relative prices of things, as well as the specific amount of money for each, will vary widely over time and between cultures. We spend our money very differently in 2025 USA than Americans did in 1950 or 1830. People in other places today or in the past spend money differently from any of those. Fantasy people in imaginary places? You can extrapolate from the known & figure it out. What's the price of pie and a pint at the Prancing Pony? What's the price of an enchanted mace, or a well-shod unicorn? I have no idea, but if i were writing them I'd have done enough research to make a guess. (I would, of course, need to figure out what currency the price is quoted in, and whether it's a fixed price or just the starting point for haggling. decisions, decisions...)
Note that prices don't exist in the abstract, they are always embedded in the economic, political, and social environment where your story occurs. Money itself can be complicated -- in 17c France you had to be able to do accounting in the official currency (the livre tournois) but many different coins were circulating that did not map cleanly or consistently to accounting units -- the actual metal value of an individual coin mattered, and in some places coins of different official value minted in a dozen different places might be in common use so your innkeeper or traveler would need to know what they're all worth in a transaction.
Every price says something about how the story-verse works. Relative prices say more, actually, than bare numeric price tags on their own. If you look at menus from the early 1900s, for instance, you will observe that the most expensive dinner they offer is often the roast chicken, while roast beef and steaks and anything pork are comparative bargains. Chicken was a luxury food in 1900 -- the birds were raised mostly for their eggs, and eaten as soup or stew at the end of their productive life. Young tender chickens didn't end up on your plate as Tuesday dinner unless you were rich. That only changed with the advent of factory farming in the 1940s.
(Also on those 1900 menus -- look for the celery. You'll always find it called out at upscale restaurants. That was another prized luxury food of that era -- growing celery commercially was very difficult before various technical & agricultural innovations made it practical at scale in the 1920s. So celery got the star treatment for a very long time. Special celery vases were sold for people to display their celery in style at a dinner party. Relish trays were also designed to feature well-cut celery, with everything else tempting and luxurious laid out around it. Respect the celery! Somebody spent a chunk of real money for those stalks!)
Leaving aside that digression -- a lot of the time, you don't actually have to know or tell the reader the specific price tag of anything. Unless you're dramatizing an account register, what's probably more significant is how the price affects your characters. Do they consider it expensive or cheap? Do they have to do extra work or build extra savings to pay for it, or go into debt, or dream about it for years while knowing it's forever out of reach? Or do they just buy it on impulse & not even check the receipt? How important is money to them at all? -- do they think about it a lot, strategize, stay up nights worrying about it and working on their budgets? Or is it easy come easy go? Are they ants or grasshoppers? Are they typical of their social group, or outliers in their finance attitudes or behavior?
