Most fuel efficient engine to pull 28ft pup trailer

Hi everybody, new here.

I'm a box trucker, but I've noticed how cheap a 28ft pup trailer is that is a wider and taller than most box trucks. Most can be had for $3-5000 as well. Where as a used box truck with a huge moving box with the same volume would cost cost $20,000-30,000.

So, I realize I'll need my CDL, but once I have it. I'll need a tractor to pull it.

What would be the most fuel efficient setup for a tractor to pull it that's a common thing to find on the used market?

I would really like a pre emissions, common rail diesel truck.

Is it possible to find an F650 with a common rail 5.9 with air brakes as a tractor already setup to pull a semi trailer? Would that be the most common fuel efficient setup to pull a little pup?

I was also thinking of getting a freightliner M2 with a 6.7 or a T300 with a 8.3 Cummins.

I know for a fact that a f650 with a 28ft moving body will get 13mpg if geared right. Would I get similar mileage pulling a trailer?

Thanks!