Ridley's Cohort said:
A reasonable argument.
But you have skirted around the question of how does one make MW mithral armor. Does it take exactly as long as making non-MW mithral armor? That would obviously be strupid.
Not as stupid as you might think...
Let's make a MW mithral chain shirt. But first, allow me a few more quotes from the SRD...
SRD (Craft skill):
To determine how much time and money it takes to make an item:
1. Find the DC listed here or have the DM set one.
2. Pay one-third the item's price in raw materials.
3. Make a skill check representing one week's work.
If the check succeeds, multiply the check result by the DC. If the result times the DC equals the price of the item multiplied by 10, then the character has completed the item. (If the result times the DC equals double or triple the price of the item (multiplied by 10), then the character has completed the task in one-half or one-third the time, and so on.) If the result times the DC doesn't equal the price multiplied by 10, then it represents progress the character has made this week. Record the result and make a check for the next week. Each week the character makes more progress until the character's total reaches the price of the item multiplied by 10.
SRD (Craft skill):
Creating Masterwork Items: The character can make a masterwork item (an item that conveys a bonus to its use through its exceptional craftsmanship, not through being magical).
To create a masterwork version of an item on the table below, the character creates the masterwork component as if it were a separate item in addition to the standard item.
The masterwork component has its own price and DC. Once both the standard component and the masterwork component are completed, the masterwork item is finished. (Note: The price the character pays for the masterwork component is one-third of the given amount, just as it is for the price in raw materials.)
So, to make a MW item, we make the item and the masterwork component seperately. Let's make the mithral chain shirt first...
A mithral chain shirt costs 100 gp for being a chain shirt, and an extra 1000 gp for being light armor made from mithral. The total base price is 1100 gp. The smith must spend 1/3 that price (366.66 gp) in materials to make the armor.
The DC for the Craft check doesn't change... For armor, DC=10+AC bonus... DC 14 for a chain shirt.
Once you've successfully made the item, you roll the Craft check for MW...
Ok. Here comes the tricky part... With Craft checks, you multiply your check result by the DC (20*14=280, for example). Add total up week by week, and when it equals the item's price multiplied by 10, the item has been completed.
So, when you make an ordinary chain shirt, you spend ~33 gp in materials, and you must reach 1000 with your checks before completing it.
For a mithral chain shirt, you spend ~366 gp in materials. But for construction time, you consider it a MW item... 1100 gp + 150 gp = 1250 (effective construction cost). So, instead of having to reach 11000 before it's complete, you have to reach 12500, even though the base price stays the same.
For a MW mithral chain shirt, add 150 to the <B><I>base</I></B> price (1250)... ~416 gp spent on materials, and you must reach 14000 before it's complete.
So, for a character with a total +10 to his Craft (armorsmith), and who is taking 10 on his checks...
Chain shirt: 3.5 weeks (one month) construction time... 1000/280
MW chain shirt: About 14-15 weeks (4 months) construction time... 4000/280
Mithral chain shirt: About 44-45 weeks (11 months) construction time... 1250/280
MW Mithral chain shirt: 50 weeks (a year) construction time... 1400/280
All in all, for this particular smith, the "treat as MW for construction price", simply adds about a month to the construction time.
So, when you think about it, there's little need to worry about the construction time of Adamantine and Mithral items. What character is going to take months off of adventuring to make one stinking suit of armor, when he can just steal one off the corpse of some hapless elf?