Prep depends on a couple of things: What you have available to work with and how much work you want to do.
Ideally, disassemble everything and sandblast. Then use a spray gun and prime, then paint.
If the sandblasting equipment and spray gun aren't readily available, wire wheel on an angle grinder will also work well for cleanup. Nothing wrong with brush or roller for painting either.
Regardless of how you clean up & paint it, taking things apart before painting will result in a better, more complete job.
IMO, because of the environment the plow is used in, going with an automotive-type paint/clear finish is really not necessary - lot of $$$ and it will still look tired come spring.
What I try and do every fall is clean up my plow, then paint it with common "rust paint" - Rustoleum/Tremclad etc. I generally spray everything black, then use a brush to paint the face of the moldboard and some highlights in red.
I have a pic of my plow just after it's annual repaint last fall in this thread:
I use a grinder and go to bare metal. Remove all rust and grind out about 4-5". This year I used Ace (which is a hardware store brand supposedly superior to Rustoleum) primer and paint. Two or three coats of primer. Two coats of paint, then 3 or 4 coats of a clear sealer. For that I used Zynolyte Premium Gloss which is a Polyurethane enamal. Seems to have worked well but really didn't have much of a workout this year. I've also bought some Fisher paint which I'll try next year.
I would suggest two points: 1. Prep work is the key to a good job and 2. The words Cheap and Good don't go together.
when i did my plow i did not have the option of sandblasting but did grind it off.but i did spray the paint and primmers off.First i sprayed an automotive typ primer first then i followed that up with a red rustoleum primmer then I did like 3-4 coats of and industrial type pain in the color green to match my truck with the cutting edge painted black.Now all I do issan prime and repaint really scratched areas then just keep giving it at least 2 coats every year and it stays looking pretty good.
I don't go crazy with mine. I just buff the rust with a wire wheel like 75 suggested and use Caterpillar primer with a brush in these areas. I do the moldboard in Caterpillar Highway Yellow (old Cat yellow) and the back and frame with Caterpillar black. The stuff's about $18 a gallon and I figure if it's tough enough for earth moving equipment, it's tough enough for snow. I do this at the end of the season when it's warm enough for the paint to cure.
I'm going to need to find a tough white paint for the Blizzard, I'll see how close the new Terex white is.
I have done 2 of my Boss's the paint was extreamly tuff. 1 blade i ground and d.a.'ed of the othere I sand blasted. Then I repainted with DeRusto gloss red paint. Look in your yellow pages and see if you have a sandblasting company localy it will save a lot of time dropping off the blade and paying a $100 bucks then grinding for 6 hrs.
After having spent hours grinding last year, I definitely agree that sandblasting is preferable if available and reasonable. Be sure you're able to completely cover all the sandblasted areas with primer within a few hours of sandblasting. At least in an area like mine where there tends to be a lot of moisture in the air.
We have Snoway's... so each spring after the plow season we pull the mulboards. We then check bolts, welds, etc. make sure everything is in good shape - fix what we need to. Wire wheel any bad rust (usually not that bad), prime and then we paint the plow frames while they're assembled. Reattach the mulboard, grease the cylinders - and store for the summer. We use Rustoleum products because they're readily available and I don't really know the difference.
In the fall we service the pumps, fluid, etc. We put the plows away one spring and didn't paint - and regretted it in the fall. There is a lot more rust five months later. Better to take care of it right after winter. Tough to juggle with spring clean ups - but a rain day usually takes care of it.