This is what I've used for years.
The Ospho Solution..(rust removal)
Heres another good one...
secrets of surface rust removal revealed
both are inexpensive (under 20.00) and remove rust but need to be scrubbed in not painted on There many phosphric acid products out there but Ospho is what works best for me. It aint as easy as painting something on but it works a whole lot better.
use an epoxy primer over it...