Many years ago I had good luck repainting rusty metal using naval jelly, then primer, then enamel. Eight years ago I had good luck with POR 15, but it was expenive.
I've read that Zero Rust is a cheaper paint and does a very good job.
I've also read that Picklex 20 is an excellent way to prepare a rusty surface for painting. I've found only one source, which charges $31.50 a pint plus shipping.
Are Picklex 20 and Zero Rust the best ways to repaint rusty iron? Who sells them?