If you are going underground through a parking lot have you considered using a trenching contractor that directional drills. I have seen the local cable company use them in a few jobs and they seemed to work out better than trenching.
They went under the street next to my parents house and were probably done in under about 40 minutes once they got set up.
The big advantage for the property owner is there is no sunken trench in their lot to deal with a year or two after the job is done. I am guessing the cost is less than the conventional break pavement, make your trench, patch pavement that a lot of contractors do.
