Is the paint that is peeling hard or more flexible? If the door is oil you can sand it and repaint it with oil, but if it is latex you can not put oil on it, and vice versa. A is more expensive because more work, but why does he want to strip it? What did he see that leads him to this conclusion? Now if you do scrape and sand it and repaint it you will see where the paint came loose before, but if you strip it you will get a new looking door. I personally would not strip it, the amount of work does not match the worth of a door. Hard peeling paint would most likely be oil, so sand and scraping should work fine. But it must get primed, and if it is peeling bad then it was most likely not primed last time, so you might have to paint it a few times over the summer, or next few years, as it will keep peeling. This is where striping would help solve that issue. Make sure it gets primed this time, with a oil based primer, Zinsser 123 interior exterior primer is good for me. The main points here is it oil or latex, was it primed, and what is your budget? I would bet it is oil and you could just scrape, sand and prime it and just plan on doing that a few times over the next few years. But should be charged around $50-75 for a repaint on a metal door. Good luck I hope this helps.

Thanks, Adam. Turns out the base paint was a high gloss paint applied by the manufacture so it is probably oil. In any case "A" corrected me saying he wasn't going to strip it to bare metal, just sand it enough to get the bad paint off and to rough up the high gloss prior to repainting.

He admitted his price was probably too high due to his overestimating the sanding time. So I went with "A" using his price as a "not to exceed" contract since he has done a lot of other work for us and does good work.