This rebar bender was posted by Walter Jeffries.

What we did with 20' and 10' lengths of rebar is to use a large tire from a road grader. I believe, remembering, not measuring, that the tire is either 4' or 5' in diameter. The rebar sprung out a bit but it was a very smooth bend. It was easy to then spring it in our out a bit to get the curve we wanted.

I did it with my 12yo son. If I were doing it alone I would make a holder on the tire with an eyebolt to hold the end of the rebar and then it would be a one man job. In the photo below his brother is helping steady the center of the bar, a pin in the tire would help there.