So the really hard part about metal armor is getting the tools. Like Kris, I started out with a piece of wood and a single hammer. You can do 22gauge steel with tin snips to cut it out and a dremel for cleanup, a piece of 2x4 with a scoop cut out for dishing and one ballpeen hammer, then you really want something to planish it against, either an anvil (you can get a small one for like $50) or the like. I recommend checking out Beviin's tutorial videos, which are listed in the tutorials section, as well as checking out the Warmaster's Workshop videos, which the chief posts on the mercs youtube page.
With minimal tools, it's a much longer process, but that all depends on how well you pick up the knack for it. I can tell you right now, after about a decade's experience, I could knock out a full kit in a little over a week if I didn't have anything else to do. Doing it in my spare time around work and such, it's taken me a little under a month to get all of the cutting, shaping and cleanup done on a full metal modern era set. Add in the extra plates from a crusader set (which I will be doing in the coming months) and it'll probably be about six weeks all told. That's not counting painting and such, of course.
Sintra is a lot faster and easier, and you can pick it up at Home Depot these days. They carry pvc sheets in 6mm (1/4 inch) format, and komatex (fpvc, practically the same thing) in 3mm (1/8 inch). You can also work sintra with a $20 heatgun and a razor knife, plus some sandpaper, compared to the tools you need for the metal work.
