The cost of the fixture, itself.
Our RV pad is in the back yard, next to the garage. (3 ft from the wall, 10 ft wide.) The incoming electrical service comes to that wall from service lines in the alley. The meter is on that wall, as is the 250 amp main service box. There was room for the new circuit breakers and capacity for the 50 amp service. The cable in the RV is long enough to reach that outlet from anywhere on the pad.
We had a 50 amp service professionally installed there. The cost was $125.00. (I did Shanghai an electrician working on a near-by house, at the time. I did make sure he bought separately, for my job. ) Took him less than an hour. Only thing I regret is that I might have had him install a 110 outlet there, as well. Would have been a good idea.
To go further than two or three feet from the meter, of course, would cost more. Also, labor rates in Idaho are relatively low. But that is one example of the cost of the service alone. Going further from the main breaker box or upgrading the incoming service would cost more.
Ray D