Pricing treasures found in fantasy RPG play can be a pain for a DM. Do you give an estimate, a flat price , require some sort of skill roll or keep it secret until they try to sell it? It can be a tricky matter and depends on play style.
I myself like some mystery, I don't want the players to be completely sure of what they've got but I'm also lazy and can't keep track of every darned item I let the players haul off.
Here's My miracle solution that let's the players have some idea of what they have without making it a fixed value.
A treasure value rated in dice and scale. Roll a certain number of dice times the value multiplier.
A Sample Treasure Value Scale
AAA... x1000 gold pieces.
AA..... x 100 goldpieces
A........x10 gold pieces
B.........x1 gold pieces
C.........x1 electrum pieces
D........ x3 silver pieces
E......... x1 silver pieces
F......... x1 copper pieces
So when players find a gem, piece of jewelry or gewgaw I can tell them it's a 4C or 5D instead of having to have a fixed price or making determining the value a time waster before it's sold.
I'm figuring a range of 1-20 dice will do the trick.
So why use letters for treasure value scale instead of a number. 3 reasons- it requires players to learn what they are dealing with, it keeps specific numbers out of players heads and the payoff can vary by location along with grade. Some markets can have better pay-offs then can be found in other markets and this can cause the size of the dice to vary along with the multiplier.
A community might have a base die and that die type might even vary by type of product and even who the seller is trying to get to buy the goods.
Brond the Barbarian is in the town of Midvale and discovers goods here sell at 1d6. Not the best but he decides to risk it anyway. He tries to unload his gem at the provisioner but can only get 1d4 there so he spends more time hunting down a jeweller who will buy at the 1d6 scale.
Incorporating skills and or wheeling and dealing into this system:
Use the basic task resolution system you like and for unopposed rolls let the player who wheels and deals well to reroll up to half the dice something is valued at.
Sal the DM likes to use CHA rolls for haggling at the market. If the player makes the roll the get to reroll the 2 lowest dice, if they fail the 2 highest are rerolled. Brond the Barbarian is trying to unload a 3A gem and makes his charisma roll. he rolls a 2,3 and 6 for the dice to find how much he can get for the gem and rerolls the 2 lowest getting him a 4 and a 3 for a final total of 4+3+6 or 13 so Brond gets of 130 gp for the gem.
A simple contest between seller and buyer can be to have the seller roll one die type larger then normal and the seller roll one die type lower then normal and average the two rolls before applying the multiplier.
Brond the Barbarian is selling a 3A gem to Jerry the Jeweler. In this market the die type is d8 so bubba rolls 3d10 and Jerry rolls 3d6. They get a 17 and 11 each so Bubba walks off with 280 g.p.
A DM could also be ambitious and price items for usual sale at his bazaars and shops with the above system. Compare the price to the grades and find a die range that feels good.
If a sword were normally listed as 10 gp a price of 3B could work well in an typical setting.