Yep, the materials cost will be 1/3 of the total cost.
For a mithral buckler, you're looking at a base price of 15gp + 1,000gp, or 338gp worth of materials.
For a mithral small shield, you're looking at a base price of 9gp + 1,000gp, or 336gp worth of materials.
For a mithral chain shirt, you're looking at a base price of 100gp + 1,000gp, or 366gp worth of materials.
Keep in mind, however, that you're looking at spending an inordinate amount of time to make these items. For a mithral chain shirt (as assuming you're a pretty standard 4th-level character), the time calculation looks like:
Variables
Base Price: 100gp
Base DC: 14 (= 10 + AC Bonus)
Mithral Price: 1,000gp
Masterwork DC: 20 (Standard)
Craft (Armorsmith) Bonus: +12 (= +7 Ranks, +3 Intelligence, +2 Masterwork Tools)
Time to Create
Chain Shirt:
DC x Craft Check sp / week = 14 x 22 sp / week = 308sp / week
Total Progress: 1,000sp
Time = ~3.25 weeks
Mithral / Masterwork Component:
DC x Craft Check sp / week = 20 x 22 sp / week = 440sp / week
Total Progress: 10,000sp
Time = ~22.75 weeks
Total Time = ~27 weeks = ~ 1/2 year
Note, also, that the buckler will take an almost identical amount of time - the determining factor is the mithral cost.
Thus, you are looking at approximately a year of your character's life devoted to doing nothing else for 8 hours a day but making these items.
But, you get a 66% discount.
