When the second game came out, I was charging $200 - 300 for the cloak alone. If you break down the costumes, you'll notice there's LOTS of pieces, which are very time-consuming to make.
The important thing to remember when commissioning someone to make your costume is that you're not just paying for a costume. You're also paying for their time and expertise.
One of the most basic rules for survival on any planet is never to upset someone wearing black leather. (This is why protesters against the wearing of animal skins by humans unaccountably fail to throw their paint over Hell's Angels.) -- Terry Pratchett