Unfortunately, the rabbi in the on-line shiur knows nothing about business.
Mass produced items can drop in cost when large quantities are produced on mechanized assembly lines and the raw products purchased at bulk discount prices.
This does not apply to hand made/produced artisinal products. A mezuzah takes a qualified sofer X amount of time to write. If he has orders for 1000 instaed of 100 the time required for each scroll does not decrease.
The sofer can only produce so much product per day and he needs to price them to provide a living for himself and his family.
This is not like running a machine and extra two hours a day to turn out another 1,000 stamped stainless steal forks or spoons.