Ok, I hav e more or less completed what I was looking for, and a couple of points jump out at me that may or may not be useful.

My personal reference is roughly the 250 CE to 750 CE era, since it was much the same before then and didn't get into major changes until around the 1100's CE.

First, get a list of trade goods. Remember that whenever there is something in a "raw" form, trade will take it someplace to turn it into something else. The easiest things I can think of to say here is stuff like Wool, Cotton, and Hemp -- where it was grown was not always where it was turned into fabric, and where it was turned into fabric was not always where it was embroidered or turned into clothing.

another example is iron ore. It would be refined in a different place than it was mined, and the ingots would then be taken elsewhere to be turned into weapons or whatever.

Your list should have three columns: what the good is, where it comes from, where it goes.  A more complex list might include how it gets there, the seasons for it (especially for food stuffs), and any notes on how prized it is in certain areas. You have to know what it is, where it comes from,, and where it is going, though because that will let you determine your trade routes. Trade routes prioritize safety of the cargo and speed of travel, in that order.

The list of goods can be as long as you want. As noted, you want to set things up for bulk -- so figure out a base "nunit" (barrels, for example, are a unit). 

Then, drop that into your treasure list. 

Really. Treasure is more than just gold and silver and copper and platinum coins. Coins are fairly rare, actually, but real wealth can be stored in goods -- much like art collecting.

I have a fairly involved one I need to assemble for my own stuff, so I hope that all of this has helped, and good luck!

And thank you to everyone else who contributed -- I ended p benefiting a lot from this!

And returning here one final time because it all got me going and I thought I would share my example. I am ending up with about ten pages of table, lol, so it will be a lot of little work, but I think it will be worth it in the end.

I still need to divide all of this into sections of Raw (raw materials, including food stuffs), Finished (any “finished” material, such as weapons and clothing and animals), and Luxury (any non-survival item meant to look nice or enhance quality of life).

• Origin: The place the good originates. Multiple sites for many raw materials. Country is usual, might be a tribe or a specific place or even just “the wilds”.
• Unit: the common size of the good when being sold: 1 barrel, 1 item, 1 pound, 12 chests, etc.
• Type: They type of good it is. Plant, animal, food, etc. Some types are things that merchants specialize in, like spices.
• Destinations: For my destinations I had to divide my setting up into seven regions in order to effectively table them. This incidentally helps me see additional connections.
• Value: This will be the base value for that item in that location, and ultimately will help me down the road when I do custom pricing by realm and merchant (adding variables for the party to consider). I use a silver piece as the base value for everything, so all of it will be in silver pieces, which allows me to break it down into the copper and bits I use "when it hits the street".

This will then tie into the Export and Import structures of the Realms themselves, showing me what they don’t have and what they have extra of that they sell.  99% of the time for me none of this will come into play, although I do have treasure that includes some very basic trade goods kind of things, and this gives me an ability to look more closely into that for role playing. Much of the existing information I already have written up is going into the table (below is just the first few lines, and yes, I see the duplicate, lol).

All of this will go into the "player Handout" chapbook I have about eh world, and will likely force me to do some changes to the outfitting section of the House Rules player's handbook. However, in the end, totally worth it, as I will have a much better idea of value for different things.

You can make it as complicated as you want, but then it starts to be a non-d&d game unto itself. 

The other thing is, the dive will be more of a randomizing friend. You can explain it away as supply chains, bad crops, a glut from another place, low demand, etc , but all that comes after randomized price generation, and the randomness itself is inherent in markets.some things may have fixed prices due to monopolies much like oil today, but if EVERY product is like that, well... You don't really have a simulated market in your game, you have fetch quests.