Every time prices are involved in isekais, MC's stupidity ranks up a notch (and that is a feat in itself)
You are bringing revolutionary innovations and your main concern are the so called fucking affordable prices? Affordable for who? By which standards?
A refrigerator in 1922 cost 700$ while a Ford model T 450$; even today prices ranges from 3700 tor up to more than 30000 tor.
Also, since it is one of a kind, you can make it cost whatever you want.
Also, also, there is no way to sell lighters for the price of 5 pieces of bread and make a profit.