re: Anybody familiar with a hosted pbx phone system?

It depends on who the provider is as far as the per seat cost. Some offer tiers of users with a different cost for each. Others give you just a single rate but fully featured seats. Regardless you'd be looking at anywhere between $15 and $30 per seat. I would stay away from Cox though. They can make all the promises in the world but I've heard it from their techs that it's a bad product and they still don't really know how to service it well enough.