"why is haddock and chips cheaper in West Yorkshire than in Whitby ?
"
Supply and demand, and a bit of market theory. The 2 markets in this example are not the same, and it has little to do with transport cost. You charge (usually) whatever maximises total profit - if you hike the price up in Whitby and folk still cough up, then you're in the pound seats. If you tried to do the same in W Yorks, you'd lose more custom than the extra you make on each unit sold etc etc

Elasticity of demand and all that I think....