I think the bottom line on rust repairs is, yes, you can but....

If you ARE going to make the effort, and it is considerable, you should really investigate the cause of the rust in the first place.  A scratch?  No problem, sand, prime, repaint.  Paint worn away by grit, etc.?  Again, no problem; maybe add a layer of undercoating before the topcoat.  But, a rust perforation from standing water will recur, unless you replace the rusted metal with a non-corroding substitute.  And little body rust flecks are usually due to deteriorating paint: little holes you can't really see, even up close, with the naked eye, but are plenty big enough for the water to reach bare metal, start corrosion, and travel along the soluble rust, furthering the 'cancer'.  The only real answer here is the total repaint, and I mean TOTAL, if the cancer is widespread.  That's ALL the body, sanded down to the metal, inspected for corrosion, repaired, primed, painted.  $3500 - $4500 is very realistic for this size of job; if it really is a good shop, you're getting a deal.

But for little jobs, beware: it can get messy.  Have you a wind-free place to paint?  If not, overspray can dull other car parts; masking the whole vehicle to paint a small fender patch isn't unheard of.  Are you prepared to use proper acrylic enamel paint?  That means mixing, hardeners, other additives; again, messy.  Has the rest of the vehicle's paint job oxidized, even a little?  If so, you can make a 'perfect' match to its paint, and the freshly painted patches will stand out like a sore thumb.

All caveats, and things that are eventually overcome by the patient perfectionist, or ignored by the care-free.  If you are neither of these, spend the Hawaii money on the pro job.

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