This is very cool! I wish there was a plus or minus number in parentheses next to the price tag to tell you how much it changed from the base.
For examples, let's say the base price for something is $40, when an island/city wants to buy it for $45, it would show "$45 (+5)" Now you know your profit for each item is $5.
I say this because it's frustrating to go back and forth between the bag and the city shop.