The realities of the distribution system are as important as all the factors mentioned above.
Kodak used to be its own distributor. Prices were relatively stable, because with the exception of shipping costs and tariffs, most of the retailers could purchase film for the same price as other retailers.
Now that there are intervening middle wholesale vendors, prices are all over the map.
The US distributor that sells Ilford to B &H sells it for less than Harman or its distributors sells to UK retailers.