Here's what I have got to repair my rust (bearing in mind, I've had some of this from when I was repairing my first 214)...
Hammerite Rust Treatment Paint (either spray can or brushed on)
Sand Paper
Rust and Paint Remover sanding block - £2 from Halfords
Primer - Spray Can
Paint - Spray Can (I've found most of the Halfords spray cans are a very very good match)
A spray can of Waxoyl
Isopon or other body filler
Basically, sand/grind down the area. If you have to make a hole in the body then so be it. Get as much of the rusty crap out as you can.
Treat the whole area with Hammerite rust paint or Waxoyl. Give it a few coats of this, sanding lightly if you use the Hammerite paint.
Use Isopon, or another body filler to fill in any holes in the body work. Sanding down until smooth with the metal.
Treat again with Hammerite rust paint (not Waxoyl). Sand down until smooth.
Two coats of primer, sanding down after each coat.
Several coats of paint, sanding down after each coat.
Two coats of laquer, sanding down after first coat.
And that should be it. Definitely worth a try and isn't that time consuming.