Easiest cheapest way to fix dent

The stuff in the aerosol cans from Rustoleum is good for what IT IS..... but not even close to quality of product from the real auto paint stores. It is very durable BUT it will not stand UV rays well at all. FADES They have a "primer-sealer" that is pretty decent. They have a self etch primer for bare metal, I have used it over old primers, and acrylic urethane topcoat. Results will vary and they do not recommend the self etch for anything but on bare metal.
Old way is filler over bare metal, but NOW best to use epoxy primer over the bare metal and filler over that, BUT I do not know a source for the epoxy in an aerosol can. Self etch has acid that can be a problem with filler. You need to apply filler over a LARGER area than the ding, and be able to block it all level, and YOU need a sanding primer for this, and correct paper, and block.
I respect your tenacity. Learn by doing, study the techniques that are all over the net, and realize all mistakes in bodywork can be corrected some easier than other!!!
Like you said, you will do it your way. Results and happiness will vary!!! Give er Hell