I am a general contractor in east Texas and pour residential slabs quite often. There are a lot of variables (some of which are geographic) but my residential slabs run about $4-$5 per sq ft. The following is a breakdown from a typical 2500 sq ft slab.....
50 yards of concrete at @ $115/yd $5750
Labor $2500
Material...form boards/stakes/rebar $2000
TOTAL $10,250/2500sqft= $4.10/sq ft
The ready mix runs about $95/yd plus delivery plus taxes. Thats where I come up with $115/yd delivered including TTL. Austin might be much cheaper.
Labor alone costs me $1.00/ft. That includes setting forms, digging footing/beams, laying steel rebar, and then actually pouring/finishing concrete. This DOES NOT include getting the site ready. This assumes you already have your "pad" built.
Material includes form boards (2x6), stakes, rebar (#3-3/8 and #5-5/8), plastic chairs to hold up steel. I use #3 rebar in a grid pattern on 18" centers then use #5's in my beams and footings.
This is the way we do it in East Texas. They have to do it different in DFW (post tension) because of their soils. Not sure how it is done in Austin.
In general, the larger the slab, the cheaper per sq ft. The smaller jobs are more expensive per sq ft.
YMMV! Hope this helps.