The F150 with an Ecoboost is a great tow truck.
But not so much for the mileage when towing (I get the towing mileage in my sig below). It's the low end torque that that justifies its higher price over Ford's 5L V8. The low-end torque (<3000rpm) comes close to the 3L V6 German diesels and is better than most big gas V8's, including Ford's 6.2L.
And when you're not towing you can get very good mileage, better than the big V8s and close to Ford's 5L V8. I get 20-21 mpgUS on our country roads.
By the way, all the mpgUS numbers I'm reporting are not just for occasional trips. They are long-term numbers, hand calculated, covering 55,000km of travel, including 35,000km of towing from Florida to Ontario to the West Coast.
But, for the light weight trailers you are talking about, the 5L will be fine. If you ever want a heavier TT, maybe up to 8500#, you will want the F150 Ecoboost, or maybe a Superduty.
Don't forget the truck's payload. With these trucks, payload is more important than towing capacity. With travel trailers you want at least 12% of the trailer's loaded weight on its tongue. That can be a lot and suck up most of your truck's payload leaving little for people and gear.
EDIT: and as for costs. My new truck cost me can$32K (less tax) in 2011 and less than $100 per year to change the oil/filter and rotate tires since then. I have spent $$ to stiffen the suspension though.
