This definitely sounds interesting. I guess I would want to know more about the project and it’s cause to know completely. Is it for public beautification?
Saying that, In my experience 2k-10k would be a round about retail (depending, like Clay said) but I would thing there are artists that would be willing to do a project for a lower rate for the right venue.
Bria Sativa Aguayo
http://www.briadesigns.net