Well, there's always one best way to find out.
The most durable kinds of paint that I've ever seen are the two-part "epoxy" paints that they like to use for marine applications... but I'm not at all sure that that is really much cheaper than paying someone to do powder-coat. There's a thread in one of the other forums where a guy had his frame, brake rotors, footpeg brackets, and various other bits powder-coated for $200... and the results look great. Keep in mind, when you get ready to do this, that you're likely to find little odds and ends that need replacing too... budget in a little bit to cover the nickel-and-dime stuff like swingarm bushings, misc fasteners, headset bearings, etc... One other thing occurs to me thinking about this... if you are going to use paint, you'll probably want to leave most of the original finish on the frame and only "scuff" it with sandpaper... that way when you do get a nick here and a chip there (and you will) it won't rust through. It's a big job, good luck!