The most economical way to deal with subframes in this area is to have them powdercoated, we have a powdercoater that beadblasts and powdercoats them for $100 in satin black and they look awesome. Full frames are running $200. A person can't do a quality paint on these parts for that price.
You can go to extremes with this stuff, Example: The next project I have scheduled is a 68 Camaro Z28 restoration and the subframe was bumped, sandblasted, then dipped and E-coated, then scuffed and epoxy primed, sanded and will then be painted in singlestage urethane. The owner is trying to achieve the best results possible. After the inside is treated with cavity wax it should last till the end of time.