Interesting question, but not one easily answered. VO isn’t my area, either, so I I’ll have to give general advice.
Yeah, I know it’s a pain, but it’s the best offer I can give. It’s actually not too difficult, just time consuming. Use those keywords “audio-book voice-over” and run a few searches. Pop open a spread-sheet and make some categories: new sellers, level ones, level twos, level threes; subcategories based on your opinion of their ability based on their samples; make a note of the number of reviews and the score; lastly, their prices for various word-counts. You don’t have to go crazy with a sample size, but I would say around 15 of each seller level.
Next is harder: self evaluation and being honest about your own skill and most importantly figuring out where you fall in that gathered data.
You have reviews, fortunately, so you’re not starting with nothing.
(I just realized I misread your question as: “I’m thinking of making an audio-book gig and want to know how I should price it.” Oops.
I’m hoping one of the other VOs in the forums can answer your question on the project price.)