I'm an RV.net professional and nothing more.
I'm agreeing with the others that based on your posts you really should hire an electrician to do the hookup and make sure you have an adequate size wire. If you have Yelp in your area search for electrician and then click on the "Request a quote" link and put in your request.
"Installing a 30 amp 125 volt RV outlet 250 feet away from main panel I will provide the trenching and materials. Paying for your expertise regarding trench depth, wire gauge etc plus to do the final hookup."
It will go out to multiple people and somebody it bound to text you some kind of quote.
Where I live trenching is about 10 dollars a foot. So I can see him quoting 2,500 for the trench alone. Call an equipment rental place and see what it costs to rent a trencher for 4 hours. Around here that's $75. If it's just plain ground with no pavers or concrete in the way you can have it trenched in under an hour. But look at the whole picture. Do you have to go through a wall, is there a sidewalk, a water line, a tree with big roots or a sprinkler system in the way?