Hello,
I think it may depend on the complexity of the visual style (and the illustration skill,) the time needed for producing one character, and the artist's hourly rate, and of course the artist's experience (an experienced artist may ask for a higher rate than someone with less experience.)
But it also depends on your budget and whether the artist can adapt to your budget or not. If they can and you're satisfied with their production then it's great, if not then you could look for another artist.
Also, question: are you looking for an artist or did you already find one?