Tariffs. What do proofreading, correction, and perfect English cost?

Some editing services quote you a per-page or per-line price.
But when an editor gives you a per-page or per-line offer, this can only mean one of two things. You’re either being undercharged or you’re being overcharged.
Per-page and per-line tariffs overcharge clients whose text is good, and use that margin to subsidize clients whose text is not so good.
Great if you’re the one getting a “free lunch”. Not so great if you’re the one paying for it.

I invoice my clients for every minute I spend on their texts, but not a minute more.
If you need to know before we start working together what a corrected text is likely to cost, I supply you with a maximum figure.

How does costing work in practice?

I look at the length and quality of your draft, at how strict your style guidance (if you have any) is, and at how tight your deadline is. And estimate how well we will be able to work together to resolve ambiguities and clarify what’s not clear.

And if a corrected text takes less time than I thought, you just pay less. It’s as simple as that.