What do you mean by that. Depends on the artist and what is going to be on it. Your description is too wide. 100-300$ since I don't know if you want it ultra detailed or like most novels with just big characters.
My current BIAW cover was 150$, my TWS cover which is even more animey is in the making and it was 100$ but has only a single character and a nice background.
Honestly, that cover isn't what I imagine a professional-looking cover looks.
The best artist I know of that draws top tier anime character design is around $100 to $150 per one character. Since you'd have a bunch of characters in a cover, plus the background, who knows how expensive it can get (he's not offering covers, mind you).