$15 per LINEAR foot (not sqft) if it's easy access and easy digging. More if we're working around bushes. Always have the customer call to have underground utilities marked before you start to save yourself some problems. One customer assured me that I was in the clear, and I trusted him. My mistake. Ended up cutting thru his cable line. Luckily, I did cable repair in another life, so it saved me the cost of a cable company service call.
I did this one for about half of what you guy's charge. But it was for a repeat customer (City) and about a 1/4 mile from my home. Still ended up about $75 pr man hour. I think I probably worked myself out of a job though, they've called me once or twice a year for the last 5yrs to trap something out of there.
$20.00 a linear foot here also and up. If an excavator is needed, the motorized kind, LOL it will be added to the job cost if practical.Materials are included in the pricing.
Our price includes materials,which is usually minimal,around 1.00 per running foot. We either use 1" X 1" heavy gauge GAW wire,or the same thing in 1" X 1/2" mesh.