What we have learnt from this discussion is that costs "isn't" costs. Costs is costs plus £X or X%, which may or may not be properly disclosed to the customer.
You dont need to discuss your costs with the customer how you break it down. You dont go to the bike shop and expect them to tell you how much they get the wheels for and how much they are making so why does it make a difference in a wheels or bricks.
If you purchase one pallet at £100 and another a week later at £110, then sure, pass that onto the customer, costs is costs