I did mine 7+ years ago and used some leftover black epoxy primer/sealer. It stood up nicely to the elements, though it did rub off where my left foot rested against it. It's a professional product so you'd have to have proper spraying equipment & a respirator as with any paint system.
You could spray or brush on POR products & likely be very pleased with the results; you'll want to follow their recommended application process, though, for best results.
If you just wanna rattlecan it & go, I'd at least put on some self etching primer before the paint to help adhesion, also making sure to thoroughly clean & prep the metal first.
Roll cages take a lot of time to do well b/c there are so many bends, nooks, and crannies to get into. Just when you think you've hit everything you'll find a spot you missed. I'd imagine a paint shop job will likely be almost as much as powdercoating....