residential, might as well figure about $450-600 per yard, graded, formed, poured, and finished.
However, on slabs versus footers, the labor gets to be less, so you may can expect down around $350/yard.
Assuming you have a 4" slab and prob. 8x8x#10 WWM, and minimal grading, you could prob. get out around $3500, maybe less as construction work is starting to get a little cheaper these days.
References? You can call Penhall. they do fantastic work, but are really, really proud of it. Let me know if you need a contact for them.