Hello.
Maybe it's very wild and unrealistic idea and I must admit I haven't thought about it very deep and long, but here it goes:
How about the player could buy a "Merchant licence for X resource" for the given amount of gold coins. When you have a "Merchant licence" the player can set the price for given resource but he must also provide non-stop supply for that resource. If other players will not agree or sell that resource lower they of course can and that may ruin the players with the license.
Probably this will put the owners of the licenses to way too good position, but on the other hand resources would be almost for free...
I was just short, because this was just a small undeveloped idea...
What do you think?
BTW: my first forum post after almost a year of being active Settler.
Nordavind...