In our area hay is scarce this year. That being the case it may be worth the effort needed to get it. But. We've tried on a number of occasions to use a hand winch on rolls. It's doesn't work very well....we've had better luck with a chain and a pickup moving them if we had to..seems they go easier at a faster speed than a winch.......
If you have a low spot that a trailer can be parked,a couple or three strong backs can roll it on to the trailer.
But around here it is just an unspoken thing that the seller loads round bails........or maybe the price can lowered to off set the trouble of bringing their own tractor. We around here didn't get a good first cutting, no second cutting and no rain in sight for a fall cutting. Having hay so scarce, even having to roll it on my hand would be a blessing.
arkiema

A winch or a come along on the front of a pick up should load your bales on a trailer.

Good luck!

Lori