Book narration is a unique talent that few folks have, I didn't realize that it was so lucrative though.
It's not as lucrative as one might think.
The standard is pay per finished hour. Not time invested. Most of my books end up between 5 and 6 finished hours of recording.
The narrator will have auditioned for numerous projects to land one. Then they'll get the manuscript. Mine top out at 60,000 words (10K words = about an hour of performance.
They then build a home studio space. Non-audio reflecting walls and top/bottom surfaces. Then they have to stop and retake if a motorcycle, trash truck etc, rumbles down their street. One narrator had to turn her AC/Furnace off while recording because she kept getting too much white noise whenever it kicked on. They actually add white noise (room noise) to the finished recordings, but it's a final step.
Now, give the manuscript a read-through, marking up the text with character notes. Each character will be performed with their voice. For one of my characters (the snarky cat who is addicted to coffee beans) - I told the narrator he's a Welsh Danny DeVito.
She sent me a character voicing file, where she read through lines for each character. Fortunately, I write in series, so narrator 1 was able to transfer the character notes for the main cast from book to book. BUT, I introduce about 6 new characters per book. That's 6 new voices we have to agree on. And not just voice tone, but how they get acted.
Narrator then starts recording. They may send me sample files or written questions if they need gaps filled in. After recording, they have to go through and edit the audio. They never nail a chapter in one take. So they might have an hour, or maybe three, in on one chapter. Probably three hours. For 12 minutes of finished audio.
I usually figure that they've got about 3-4 hours of work per finished hour of audio. That's 18-20ish hours for one of my books. That's about $40-50/hour for self-employed "talent". They deserve far more for putting up with some of the tripe we write.
But, during the pandemic, too many small theatre groups were out of work. That's how I found one of my narrators. I was lucky that she's a dual citizen, and has a good understanding of Brit dialects for my Welsh series.