A hydraulic auger is far stronger than any of the normal gas augers that you see at rental places so it will drill down very well. Being machine mounted, I can put a lot of downforce on the bit. Depending on what you hit, it can be cut up (like roots) or pulled up (rocks) etc. In the case of big rocks, they can be excavated or hammered with the hydraulic hammer.
Being hydraulic, it also can go in reverse so there won't be any stuck bits like the gas jobs deal with.
How much per hole? - LOL I still can't see underground so I still do it by the hour. I have dug 50+ holes in under an hour and I have had 5 holes take 2 hours. There is no telling in NH. AAGR, I say figure 5 minutes a hole.
Regardless of if you have me do it or not, call Dig Safe http://www.digsafe.com/ ahead of time and have them come out and mark any utilities. They usually want a 2 day lead-time, it is free and you won't find any insured people that will do the job without calling Dig Safe first (it is a requirement for commercial liability insurance in NH). If they don't mention Dig Safe, look out.
I am in Merrimack and will travel locally. I am fully insured and I charge by the hour. To keep the payment simple for everyone, I prefer to be paid in cash.