OK, my guess before I called anyone was about $6000 to $9000. I was a stair carpenter my whole life and I hate to waste peoples time with getting a ton of estimates so I wanted to see if I was off base.
I had one guy come over, his price; $9000 to demo and haul. $8000 for concrete and labor. $850 to finish grade. Total; $17,850. Keeping in mind, this is as described, nothing fancy, nothing difficult, just flat grade, 1500sq ft. I figured the concrete was about $2000 to $2500, so it seems $15000 in labor was high. That was with no rebar or mesh.