Well, just a quick estimate, I have pulled/replaced the engine in my car in less than 10 hours. That was taking my time, and all I did was pull engine/tranny, separated engine/tranny, change rear main seal, reinstall in car, hook up hoses, wiring, fill/check fluids, and have it back on the road. I would think that would be the least a shop would say would be involved in the labor, especially if all they are doing is pulling and replacing the engine, no seals, extra removal of parts for maintenance, etc.
With that said, give a safe estimate of at least $80.00/hr for labor and you're hitting $800.00 before tax.
But, if you have an engine and tranny you know is reliable and can just do a simple swap, they probably can do it in less time.
My only suggestion is before you put in another engine, check for any leaks and if anything needs to be replaced (seals, timing belt, water pump, etc.) do it yourself before you put the engine in the car. Good luck!