The going rate used to be $1.50 per square foot to pour and finish, that did not include prep, forming and concrete. I would figure at leat another $1.50 to $2.00 per square to prep and form depending on what is needed.
Concrete is going for $100 to $110 per yard give or take; for a 4" slab you need a little over 2 yards so figure 2 1/4 yards. You may have to round up to full yard increments. Less than 5 yard delivery, plan on $50 "haul charge."
You're looking at around $400 if you do it yourself and rent tools. If you want fiber mesh, hang #4 steel, need fill, etc this may need to be a little higher. I think Fiber is about another $7.50 per yard. I would anticipate $1000 if you simply write a check. If you talking to a small company or an individual, definitely throw out the "what's the cash price" question.