Price of a new F250 Ford ? Good or bad?

I don't think you will be happy pulling that size trailer with the big gas engine. I had a 2015 with the big gasser. It had to work pretty hard to pull our 26' TT in hilly country. The engine does ok, but you will not get there in a hurry, you will endure a lot of engine noise as it downshifts a lot on even slight hills, and fuel mileage is terrible. If you still want the gasser, I would say a price in the lower 40's for that truck is pretty fair.
I traded mine for a very low mileage 2016 Powerstroke. Got it for under 40, out the door.
Look for low mileage used. You can save a ton of money up front.