Im thinking like $40-60 per page. Considering your only looking for flat colors on cleaned lineart and tones, I'm thinking around part time wage of coloring work. A typical turnover is a page a day so considering an 7-8 hour workday a page will put you in the price range.
I think for loose lineart and no tones the rate per hour would increase closer to industry price ranges, which I gander between 15 to high 20 per hour.
These are pretty conservative estimates but from a commissioner market, this might be what you'd negotiate for.