Determining the prices and availability of goods in a Grotty age will set the tone for what the players will have their characters strive for. The average character will is assumed to start with roughly 100 groats worth of goods and gear on hand and as such they will tend to be limited to items of low quality and dubious functionality.
In a grotty age much of what there is has been around for a while, that which hasn’t is recycled or quickly despoiled by the general environment of verdant decay. Gear and grub are always going to be dear and one can’t be sure the coins in their rotting purse will be of much worth in a few days or mayhaps be a fortune to someone in need of selling off ill-gotten gain.
Finding a Base Price by converting prices from other sources:
Duff goods costs1/2 the number of standard D&D price in g.p. ibut exposed as Groats
Shonky goods cost the same number of groats as g.p. normally listed.
Bodge goods cost x2
Fit goods cost x5
Brill goods cost x20
Ace goods costs x50
(if your source material uses a silver based economy a groat should be considered to equivalent to a s.p. instead of a g.p. for common goods).
Example: if the core riles beign used show a Sword to be 10 g.p. in a grotty age campaign a Duff Sword could be had for as little as 5 Groats or an Ace Sword could be had for 500 Groats (well outside the range for most characters starting funds).
It should be apparent from the conversion guidelines above a well made steel sword would likely classify as a Fir of Brill purchase and cost a good bit of coin.
If your prices are under 1/10th of a Groat it is recommend to express the price in Gubbins.
Between that and a whole Groat prices will likely be stated in Spangles and Baub. Much over a dozen groats and it is likely prices will be given in Lucre or Marks. While Gilders and Zlotz are valuable it’s unlikely anyone would express prices in units of such coins.
When coming up with pricing to fit a particular campaign the GM is encouraged to consider the following:
Keep in mind it is vaguely possible for a person to get by on 3 groats a week if they don’t mind sleeping packed in a leaky shed, eating cabbage soup of dubious character and drinking hootch that has a chance of blinding them.
Food is precious but cheap. Because of the general conditions of things food doesn’t last long typically and is priced to move unless well preserved or a rare luxury. When converting the prices of common food items (in often inflated prices of gamebooks) it may be necessary to reduce the rice to 10% or less of normal prices before adjusting for quality.
Drinks and smoke will prove to be more valuable more often as they tend to preserve a tad better. Unless beer has soured really badly it will still get you drunk, and a dry powdery smoke will still provide a few puffs.
Above drinks and smoke at least at the base end of the scale one will find colognes, perfumes, and nose-snuff to be of moderate value as folks seek to distance themselves from the decay around themselves.
Tools will run a wide spectrum in pricing with precision tools begin far more expensive than common ones.
Weapons and Armor will run from affordable to dear in pricing. Materials, age, method and origin of construction should all be considered when deterring true quality and price of such important goods.
Above more common weapons and armor will be magical items and technological artifacts the pricing for which will be steep but lower than one may expect in more traditional campaigns because of the general dysfunction of the economy and the cruel fact that someone with enough coin in their pocket may have enough muscle to take an item and keep their coins.
Medicines, balms, slaves, unguents, tonics and poultices of all sorts are available with a wide range of effectiveness in treatment for a wide range of conditions, diseases, and disorders. Prices will vary wildly from one place to the next but times from more reputable sources will fetch more coin than those foisted by unknown snake-oil peddlers.
Gems and precious metals do have value align with works of art and curios but the intrinsic value of such items will vary wildly base don the needs and tastes of the purchaser. A gold bar is certainly useful and will fetch a fair bit of coin but a golden goblet that can be seen to be mostly pure will likely fetch a better price from the right person. While such items are of value that value can not be certain from place to place.
Don't forget clothing, certainly not footwear folks walking about in a grotty age would likely want to keep their feet of of the general effluvium and detritus of ages. This author has found starting player characters off with lowly footwear provides a strange motivation to improve their lot on life by purchasing or thieving a pair of good boots.
Applying Variability to Prices.
In a grotty age prices in the market are nor set in stone from week to week or even day to day the challenges placed peddler will cause fluctuations in pricing.
When prices are expressed in single units the price can vary in either direction by 1d4 coin.
When prices are express in units of 10 the price can vary 1d20 in either direction.
When prices are expressed in 100;s the actual price may vary 1d100 in either direction.
In the rare case prices are expressed in thousands, leave them as they are but keep in mind items priced in 1000's and above will be very rare and seldom for sale.