Hi, this project sounds interesting.
I'm a freelance graphic designer/illustrator who has enjoyed doing a few maps for homebrew worlds. I've used Google Earth with recent projects as a base to make locations more easily user-editable, and to deal with the issue of scale, but that is just an optional.
My previously finished project -- Feedback
My very ambitious and therefore very slow personal map project
My Porfolio, (some of the same stuff and also non-map stuff)
I don't really know enough about the scope of your project to give out hard numbers -- it would probably be in the hundreds of dollars. The main question is the level of detail. If you could figure out how many normal sized sheets of paper the maps you want would fill up, with the labels no smaller than the print in an ordinary book, that figure would be a good start for me (and other cartographers) to figure out how much work this project would be.
Do you mean you want a way that you can update the maps, or you want to work out a deal with the cartographer to do regular updates?Finally, there needs to be a functionality for updating these maps to reflect fairly common changes in political boundaries and less common geographical changes. How this functionality is implemented is negotiable.