There are alot of variables. Is the area where you want the pad level? Does it have to be cut out with a bobcat or something. Do you have a place for the dirt to go or will they have to get rid of it. Usually you can get a square foot price to finish over the phone. I cut out the ground, formed my own pad, installed the gravel and leveled it. Then I paid 75 cents a square foot to have it finished. You need roughly 13 yards of concrete(85 dollars a yard here) if your pad is 4" thick, plus a load of washed gravel as a base.($200) I know its broad but somewhere between 4 and 6k. Get a couple of bids, but worry more about the concrete guys reputation than his price. If the cheapest guy makes a mistake its permanent!