Generically the time/cost of crafting is based on the target number, and the resultant skill check.It's Skill Check x Target DC in Silver each week, or in copper per day if you're in a hurry.
Assuming average costs (2d4x100 == 500), and average armor (DC 15 to craft), the minimum progress per week will be 225 silver, or 22.5 gold. So that's 21 weeks.
Optionally, a crafter can voluntarily raise the DC by 10, presuming he has the skill, and/or the established workshop, masterworked artisan's tools and/or assistants to do Aid Another. At a DC 25 the yield is 625 silver per week, or 62.50 gold. Now you're down to 8 weeks.
If he's good enough to raise by 10 again, making the DC 35 (probably reflecting a master craftsman with his full shop dedicated to the job), he'll produce a minimum of 1,225 silver worth of work per week, or 122.5 gold. Now you're talking under 5 weeks.
Time will go down as the craftsman's skill goes up, but it will still be time measured in weeks, if not months.
(Alternately, Fabricate will do the job in under a minute.)
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