Hmm, tough question - for me it would totally depend on what the page's content is and what the desired coloring style is - a pin-up or landscape for example is waaay easier to color than 7 detail-filled panels, and the flatter/simpler the coloring style the less time it takes; artificial-looking styles also tend to be faster than fantasy or photorealism. I personally might ask anywhere from $10 to $60 to color a specific page in a specific style.