You should be able to find a 2011 or so F-350 with a 6.7 diesel used in decent shape for under 30K with a warranty. I've had mine since new in 2011 and it has been trouble free. I've changed fuel filters and had one issue with an emissions glitch that was still under warranty.
It has tons of power and cruises everywhere effortlessly. If you needed a nice truck to haul an AF990 this would be my pick. You do not need a dually in spite of the advice of some here, you do need to add airbags and buying a truck with "camper package" and/or heavy duty suspension options is a must,