Hey SS: I realize it may be on the back-burner for now but I have some thoughts on a barter system. For the record, I've never actually played in a game that used such a system so don't take my word for it; these are just my thoughts. As I considered the potential it made me thingk a couple of things:
A) why have we not collaborated on anything yet?
B) this could get complicated…
In my opinion, a barter system should be simple enough that it doesn’t require numerous rolls to determine the value of a trade item. I think one way to achieve this is to look at both the monetary value (the item/objects list value in silver/copper for the setting) and modify according to regional supply and demand. It is a simple concept but there are four basic rules of supply and demand that everyone probably knows already but I will put here anyway:
1. If demand increases but supply remains unchanged, it leads to higher price & quantity.
2. If demand decreases but supply remains unchanged, it leads to lower price & quantity.
3. If supply increases and demand remains unchanged, it leads to lower price & higher quantity.
4. If supply decreases and demand remains unchanged, it leads to higher price & lower quantity.
Now that you’ve had my dime store economics lesson, read on….
It would take a bit of work up front, as you would have to re-work item lists so they’re regionally-based and have added columns for ‘supply’, ‘demand’. Each of these added columns would provide a modifier to the list value of the item in question.
Determining the availability of a resource in a given area requires some thought. Consider the component elements of trade goods (wood, steel, iron, stone, textiles, etc) and how easy they might be to acquire in the area. For example, because rocks are plentiful and anyone can go out and find a cartload of them if they wanted to, their supply would be classified as ‘ordinary’ and their demand would be set as ‘none’. Probably not the best example since they have no value to modify out of the PHB, but you get the idea.
In an area where steel is unheard of, and supply is non-existent one might first be inclined to think it would be much more valuable than iron but you have to consider demand as well. If the locals think iron is just fine, and haven’t seen the virtues of steel for themselves then demand will either be ‘none’ or ‘low’ at best. Now, if you can convince a few key people in the region that steel is much stronger and lasts longer and requires less maintenance than iron, well you might see those prices being driven up.
Which leads me to the next part of barter-system development which is the social interaction component. A good barterer should be able to affect change in the value of an item by convincing the person they are bartering with. More on that later…
As far as coins go - any high value material could theoretically be made into coins. I'm fond of the historical Chinese examples, and think they could work well in a late viking-age setting myself. Below is a link to some historical information regarding viking coins.