by the hour is not a good way to charge, myself and my friends used to charge 3x the cost of the figure, but at current costs that is not realistic either.
There are so many factors that affect cost, complexity of the figure, number of colors being used, has the figure already been prepped (mold lines etc) and primed?, has it been assembled and mounted on a base? is it something you want to paint. Is there a time frame requirement? Is it going to be basic tabletop, somewhat higher level, or very display quality? How badly does the owner want it? I personally for a long time requested 3 of each figure (3 complete units) when I got done the owner got to pick the figures he liked the best and we were both happy. I hope this helps. steveb