Just to be fair here, I searched "iPhone 7 battery replacement" and clicked the first result. I chose iPhone 7 because I feel it's old enough that people are likely to replace those right now. I just replaced mine a few months ago. This is the first result.

$18.98 for the entire replacement kit that includes screwdrivers, tools to pry the device apart, and display adhesive to make the device waterproof again. The seller is a 3rd party seller (not Amazon) and it's a highly competitive market. These prices are likely close to cost. Over 3 years, most people will spend more on earbuds. I really don't think you have an argument here.