Well, also take into consideration the quality of work he'll receive. I haven't a clue of how good/bad you are, but you do, so I guess be fair.
With the numbers being thrown around at this point, I would definitely get a deposit up front. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif