Really depends on where you are, and/or if they are professionals or just general labor.

General labor can be any where from $8.00/Hr per person to $20.00/Hr per person.

Professional labor can be anywhere from $20.00/Hr per person to $100.00 per hour per person.

But if you haven't offered any "Hourly" cost, give them a project cost. How deep by the way? A few feet down should only take a few hours. I would say $50.00.