| Teremak |
You know, I think you just figured out the key to how this item was priced, Weables.
The +5 armor bonus and SR 18 are equal to a +9 armor property (81,000 gp).
The +4 resistance bonus is 16,000 gp, + 8,000 gp for secondary.
The +2 bonus on caster level checks is 10,000 gp (about the same as a feat in 3.5), +5,000 gp for secondary.
Final cost is 120,000 gp. You get a 30% reduction in the price of an item for either a specific class or a specific alignment. Which would be 80,000 gp. Book price is 75,000 gp, so I guess they just added that extra cut since the robes require a specific class (well, one of two specific classes) and a specific alignment!
So, to make it a +5 armor, +5 resistance RothAM the final price should be around 85,000 gp. And if we added another +1 special ability, that would add another 20,000 gp (approximately) for 105,000 gp.
Right?
MA
I ran across this post and I didn't like the math. The numbers were too far off... however each ability is actually a duplicate ability of a different kind, increasing costs by 75% rather than 50%. When you factor this increase in, and apply the 30% discount *twice* (one from the alignment restriction, and again from the arcane class restriction), you get a number much more in line with the final price (assuming +1 bonus on caster checks is indeed 5000g per level).
Spell resistance - 10,000 gp per point over SR 12; SR 13 minimum
Save bonus (resistance) - Bonus squared × 1,000 gp
Armor bonus (enhancement) - Bonus squared × 1,000 gp (also the same formula used for Bracers of Armor)
Caster level bonus - 5000g per level
SR 18 = 60000g (primary)
+4 Resistance = 16000g (12000g for secondary)
+5 Armor = 25000g (18750g for secondary)
+2 Caster Level on checks = 10000g (7500g for secondary)
= 149250g Total
-30% (arcane caster requirement)
= 104475g Total
-30% (alignment requirement)
= 73132.5g
Which is really close to the 75000g for this item.