Have you tried looking at how EVE Online does it? The idea you describe roughly matches my experience in it, though I was never a dedicated trader exploiting arbitrages. As a manufacturer, though, I'd often be able to ascribe price fluctuations to externalities like, "Alliance X just won a war in region Y and now they're consolidating their gains, resulting in purchases of lots of starbase construction materials, which I'm making." Or even simpler ones like "Corporation Z seems to have come back from hiatus."
