OK, so I plagiarized Henry Ford just a bit.
I was photographing this senior in a baseball theme, and they happened to have a white van parked right where I wanted it... to reflect light.
So not only was the reflected light no cost to me... so was the reflector. The nice thing about a eflector like this is that it's somewhat mobile... and most midwest winds won't blow it over.
Photographed with a 300mm f2.8 lens.