I've had more than one quote for $400 just to dig holes. I finally found a local young man that does it for $50 for simple stuff.
I would not be able to even get a permit for $50, and that does not even include my minimum $95 permit acquisition fee. If the
sign was local I would also charge a minimum $95 site survey fee. I may have to charge another $95 if I can't mark the site for JULIE at the same time I do the survey (in my area JULIE requires I actually physically mark the site, a new requirement as of last year). In addition, I would never hire a person with no general liability insurance, as the liability would pass directly to me if anything happens (I seriously doubt your $50/hour guy can afford insurance at that rate). I require a current, in force certificate of insurance for all my subcontractors.
$400 plus the cost of the permit sounds about right to dig a couple of post holes below the frost line. More if I have to haul the dirt away. Add the price of the
sign, posts, hardware, and installation labor to that.
Despite my prices (or maybe because of them), I get a lot of real estate work. I work with my clients to find efficiencies and get them the best price I can. All the $50/hour guys disappeared years ago. I'm still in business after 45 years.