As an artist, I usually do a commission if I'm paid upfront, but will waive that in rare cases. With a group of people making a single commission, the money would DEFINITELY have to be upfront.
That said, the idea of say, hiring someone like Jeb or Rex to do a pin-up of a character, and having half a dozen or so guys band together to do so is not a bad idea. There are some people out there who ARE quite happy to purchase commissions, and if they all got together, they could actually get more commissions, as well as allowing them to commission a more elaborate piece such as a comic or what not.
I think you could be on to something here, so best of luck with it.
