Michael Curtis ask his readers about using the Silver Standard.
I used it for over two decades now including in my current Swords & Wizardry campaign.
The basic coin is a silver penny abbreviated as d or denarius. The old roman term for the coin. So 20d is 20 silver pennies.
The silver penny weighs 250 to a pound.
I have two large value goings. The first is the gold penny worth 20d. It's weight is also 250 to a pound. The second is the gold crown. It is worth 320d and weight 16 to a pound. The gold penny is not a common coin. I generally only use it for ancient hordes found in the ruins of past civilization. The gold crown is the common high value coin used both as a unit of accounting and actual coin.
There is another rare form of currency which is the silver mark. It is a 1 lb bar of silver stamped with a mint mark worth 240d. If you wondering about the discrepancy in weight is because the silver penny is debased slightly to produce a more durable coin. Hence you get 250 of them out of a lb of silver. The gold crown is heavy enough that this is isn't an issues so it is a nearly pure coin.
There is also the farthing. There are 4 farthings in a silver penny. It could be a copper coin but in the Majestic Wilderlands (like Harn) the silver penny is minted in such a way to make it easy to divide into quarters. Things like a mug of ale are priced in farthings.
The cornerstones of my silver system are silver penny and the gold crown. I find having single standard unit of currency paired with a really high value gold to be ideal. Price lists are simple with everything in a single coin. While when gold is found in the form of crowns and sometimes pennies it is appreciated by nearly every players for it's value.
For example in the last session of my S&W campaign the players have a stock of valuable art they gained on an adventure. Tim of Gothridge Manor taking Dwayne's security measures a big lightly until the appraiser came in. When he told them that the lot could fetch up to 800 crowns both Tim and the Rusty Battle Axe were on-board about making sure it is secure. Back when I was running AD&D, 800 gp didn't have same draw dropping result as 800 crowns.
The basis of my price list is from Harn which is based roughly on prices of 12th century England. You can download a copy from Columbia Games here or from the War Flail here.
You can download the version I use from here. It also include a herb list adapted and expanded from the list of herb Harn has. The effects are written for use in Swords & Wizardry.
I also found that the prices in Swords & Wizardry and similar clones are in the ballpark with the Harn List. Simple multiply by 10 to get the value in silver. For things priced in copper I just round to the nearest copper. Where this helps is not so much the ordinary items but when you get into building castles and magic item prices.
For gems the prices are it's weight in carats SQUARED times a factor based on the gem type.
For example Quartz the factor is 5d. So a 10 carat Quartz gem is worth a 100d. Amber is 2d, Agate is 10d, Diamond is 800d, Emerald is 700d, and Ruby is 1,000d.
I been busy with work related matters this weeks and plan to resume regular posts on Saturday with finishing up the Dungeon Crawl playtest and getting another "How to build a Fantasy Sandbox" post up.