I agree about the showcase models. This is a totally different category and the price is "Market Value". A masterfully painted miniature can be worth a LOT.
Regarding rank and file "table top" quality painted figures, they take me about 1-2 hours to paint (though I typically work a squad at a time). I haven't done any work for "hire"....but have done squads as gifts. The cost really depends on the value of your time. If you'd spend that time as family time or work time otherwise, then it's very valuable and probably not what someone would want to pay (if I compared it to the money I'd make doing IT work on the side for the same block of time, for example). Now, if you really enjoy painting and would spend the time doing it for yourself for fun then you're an ideal candidate for painting for hire.
I have always liked painting my own figures, but I have an awful habit of getting 50-75% completed then not finishing them up. They end up getting chipped and done over. I've got at least 15 squads like that just now. Pretty lame on my part....LOL
What would I pay for a painted squad? Hmmmm....around $30 I guess (if nice). If they were *really sweet* I'd pay more...customized "showcase" stuff? For the right figures I'd pay a lot (but I'd have to really want them badly and they'd have to fit in well with my other figs).