I am trying to come up with a budget number for a concrete slab.?

Plug in $6.00 per square ft for a budget (turnkey) and then shop bids. You should be able to get it done cheaper. I am in Texas as well and I can get it turnkey for about $5-$5.50 5" pad with perimeter beam of 12" 3000 psi concrete and #3 rebar 16" o.c. each way.