how do you price enchantments with specific costs?

[Bandw2]

specifically

if i have a +1 glamered(+2700gp) breastplate or whatever, how much does it cost to make it now +2?

does it go from +3700 -> 16K(+4 enhancement)
or is it now 3700 -> 4k(+2 enhancement)+2700=6700

[Ashram]

As far as I remember, you ignore anything that doesn't have a flat bonus attached to it.

It'd simply be as going from +1 to +2, only the total value of the item also has the glamered cost added to it.

[kestral287]

As Ashram said. It's the cost between a +1 glamered breastplate and a +2 glamered breastplate.

[James Risner]

I totally didn't follow most of that.

Glamored is 2700 gp?
+1 breastplate is 1000 + 150 + cost of BP?
+2 breastplate is 4000 + 150 + cost of BP?

So cost to upgrade a +1 glamored breast plate to +2 glamored breast plate is:
2700 + 4000 + 150 + cost of BP - (2700 + 1000 + 150 + cost of BP) = 3000

[Nuclearspatula]

James has the number correct, but is doing unnecessary math

There are two kinds of enchantments you can put on a weapon or armor:

Enchantments that have a + value (+1, +2, +3, etc...)
Enchantments that have a flat money value (2700 gold)

When upgrading you NEVER count the value of the original item, only the value of the enchantment.

When adding to an item that has both, ignore all flat money value enchantments.

CRB page 461, table 15-3 has the prices.

A +1 enchantment on armor is worth 1,000 gp
A +2 enchantment on armor is worth 4,000 gp

The value of the armor (including masterwork), and the value of the glamor enchantment don't factor in.

You pay the difference between value of the +1 enchantment and the value of the +2 enchantment

3,000 Gold