I can offer something for free that costs me money, or I can charge money for something that costs me nothing.
"If I pay money for this, I want someone to suffer for an amount of time proportional to the amount and frequency paid" is not a healthy or helpful attitude in my opinion. (It is, however, the basis of most employment, which explains the constant confusion on this matter.)
Anyway, just want to say that you don't need to change your business model to satisfy people who complain on forums, and you don't need to justify the price or business model with your work or time or suffering. The value of the product is sufficient!