To help, I simply created a Google spreadsheet that my friend (or anyone on their team) could access and input information from the in-game ports.
All it took was a spot for each city and item, and a little bit of conditional formatting.
It very quickly becomes easy to see where to buy something for very cheap, indicated by red, where to sell for the most turn around, indicated by the dark green, and where certain items were out of stock, indicated by a light grey.
The only downside is, it's very time consuming to input all off the information, and you will only have as much information as you personally gather, by going to each port.