I just had a 12x80 x4" pad done for $2300 thats with me doing 100% of the prep work, base agg, grade, drains ect.
Theres lots of "residential" type concrete guys who are hungry right now, dont be affraid to call around and ask. if you can do all the prep work yourself you will probably get a quote over the phone, if not they will probably need to see it first. Estimates are usually free.