I don't remember seeing the previous discussion, but generally the rules answer would be: "there is no rule for this". You
can try to deconstruct the price of the celestial chainmail....and you will often be left with wacky results.
Celestial chainmail (22,400gp) has more than just "mithril properties". It has:
- +3 Armor AC bonus (9,000gp property),
- a maximum Dexterity bonus of +8 (4 more than mithril chainmail),
- an armor check penalty of –2 (reduced by 3, same as mithril chainmail),
- an arcane spell failure chance of 15% (5% better than mithril chainmail),
- is considered light armor (same as mithril chainmail),
- the wearer can fly on command (as the spell) once per day(3*5*1800gp*1/5=5,400gp property),
- and the wearer must be good (perhaps meaning a 30% discount on market price)
As the prerequisites do NOT require a set of mithril chainmail, the armor should be priced based on a regular ole masterwork Chainmail (300gp). Then we add the armor's three "abilities":
- +3 enhancement bonus to armor,
- Fly 1 day at CL 5 (5,400gp), and
- Max dex of armor increases by 6, ACP reduced by 3, ASF reduced by 15%, treat as light armor (best guess at price of this ability is 10,000gp).
Then we just add it all up, giving the two lesser costing abilities a 1.5 multiplier as they are being added to a "slotted" item. Then take off the 30% discount for the magic item only being useful to Good creatures.
150gp (chain) + 150gp (MW) + [10,000gp(Max Dex, etc) + 1.5 * 9,000gp (+3 AC) + 1.5 * 5,400gp (fly)] * 70%
= 22,420gp Market Price
......which is close enough to the DMG price to call it even.
SIMPLIFIED BOTTOM LINE: It's quite possible that a Celestial Breastplate, with a +3 enhancement bonus to armor AC, the ability to fly 1/day, and (Max Dex of
+9, ACP of
-1, ASF
10%, treat as light armor) is only 50gp more than the Chainmail version.
Cool, huh?
Then again, why would anyone ever get the chainmail (DMG, core) version, if this were so?
