Hmm... so Mithral, Hellforged Chain Shirt + Hellforged Buckler + Hellforged Dastana + Hellforged Chahar-Aina can potentially give a +15 total bonus to AC?
Hellforged doesn't work on shields, and Hellforged lowers max dex bonus. As such, it's really only good on Chahar-ainas and Dastanas, which have no max dex listed (Hellforged explicitly doesn't do anything to that), but still get the bonus.
Using the Master's Forge feat and Hellforged, you could get the following:
Mithral Chain Shirt (Reinforced and Segmented) + Hellforged Mithral Chahar-aina (Reinforced) + Hellforged Dastanas (Reinforced) + Buckler (The Master's Forge thing doesn't work with shields, only armor) . +10 AC, +12 AC with an adjacent ally, counts as light armor, max dex is +7. Note you'd have to count as a Devil to do this (which has its own advantages, and Savage Species could help with this via the rituals).
Note that the Reinforced quality costs 800gp for Light armor (1kgp for medium, 1200gp for heavy) and increases the weight by 10% (minimum 2 pounds). Segmented increases the max dex by 1 for 200gp on light and medium armor (300 on heavy). Another option is Vital Coverage, which costs 200gp for light armor (400 for medium, 1k for heavy) and gives +2 AC against critical hit confirmation.
So, a Mithral Chain Shirt that's Reinforced, Segmented, and with Vital Coverage would be pretty tough to make (DC 42 to make the masterwork component), could be made at level 10 (you could make it at level 5 without Vital Coverage at DC 35), and would cost 2300gp (1/3 that to craft it yourself). It would give +5 AC, +7 max Dex, and an additional +2 AC against critical hit confirmations. Another option out there is Caster Armor, which lowers spell failure by 5% for 400gp, and can be combined with Thistledown Padding and Feycraft or Githcraft to remove all arcane spell failure.
A Reinforced Mithral Hellforged Chahar-Aina with Vital Coverage is about 3kgp and provides +2 AC, with an additional +1 AC when an ally is adjacent and +2 more vs critical hits, and has no penalties. Note Mithral is only needed if you want this to count as light armor, but it being light does make Reinforcement and Vital Coverage cheaper.
Dastanas with the same mods provide the same benefit, except there's no need to make them mithral so they're about 1k cheaper. Note that you can't stack the enhancement bonus of the Dastana or Chahar-aina with the armor's enhancement bonus.
If you crafted all this yourself (man, the Fabricate spell is SO USEFUL), then threw in a +2 Heavy Shield and had the shirt enchanted as a +2, you'd be spending about 11kgp for +14AC (additional +6 vs critical hits, additional +2 with allies adjacent). Really good for a Factotum or similar... a dex 24 Whispergnome with this stuff would have an AC of 32 this way without even dealing with other AC raising stuff (34 if he can stay near an ally). Slap on an Amulet of Natural Armor and Ring of Protection, and he can run around with an AC of 34 (36 near allies). That's enough to matter, and we really haven't spent very much at all on AC (we're using a shield, though). Total cost is 15kgp. Gotta figure out how to temporarily count as a devil though. Note that this gets MUCH cheaper if a caster in the group has Reach Spell and Chain Spell to cast Magic Vestment... a Pearl of Power is only worth it when the caster can get to CL 16 or so (+4 bonus for 9kgp... still not great).
Anyway, I think AC 34 (+2 with Adjacent Allies, +6 vs Critical Confirms) is quite handy at level 10. And at 15kgp, it's not a bank breaker. It's certainly better than a Minor Cloak of Displacement for most of the attacks you'd be getting hit by. Plus, this is just the light armor version. And obviously throwing spikes on the shield (+1 Defending) along with a Tooth or Leraje or just a nice Chained Greater Magic Weapon from a friendly caster can jump that value up nicely.
JaronK