Based on the on what our cost of machining is, as well as talking to our machine shop, you can easily get to a minimum of about $50/hr for a big expensive machine taking up lots of space and power.
Guys with big routers, much higher end than the Shopbot, they tend to charge about $180/hr.
At the core though, I think it’s wrong to charge by the hour unless you’re a big shop with a well defined process. Having been in the prototyping / model shop world for a long time, we billed a flat rate based on the job. Sometimes we padded it a lot because we had experience or equipment that made the job a simple thing for us. Other times, we took the shop rate and just estimated the time. Nobody wanted to have a variable bill that depended on time- they wanted to know ahead of time what the cost was.
I doubt the machine itself is the true value you can offer. The ability to take a sketch and make it in real life is a pretty big deal. That includes some thinking, some CAD, material knowledge, and machining, and it’s a pretty rare, and valuable, set of skills.
Rob