Mithril Breastplate vs Chain shirt

[Erosthenes]

I am debating the purchase of a Mithril breastplate.

My character is a 5th level (4 Rogue/1 Fighter) currently equipped with a +1 chain shirt.

If I have the math/process correct it will cost 8200gp to purchase a Mithril Breastplate and have it enchanted to +2, 6200gp for +1 Mithril Breast Plate. To increase my chain shirt to +2 it will cost +2000gp to add the additional enchantment. (It is already enchanted to +1 so the increase difference is +2000gp) Do I remember it correctly? I am having a brain flatus, and cannot find where the rule is to confirm my thought.

The debate here is - to Mithril Breastplate or not to Mithril Breastplate - that is the question?!

ANY help is appreciated in advance!

Eros

EDIT: I have about 5267gp and I can also purchase a +2 Cloak of Resistance and/or a +1 Ring of Protection. I do not have a cloak or a ring item.

[Grick]

Chain shirt, 4 AC: 100 gp
Masterwork Chain shirt, 4 AC: 250 gp
+1 Chain Shirt, 5 AC: 1,250 gp
+2 Chain shirt, 6 AC: 4,250 gp

Breastplate, 6 AC: 200 gp
Mithral Breastplate, 6 AC: 4,200 gp
+1 Mithral Breastplate, 7 AC: 5,200 gp
+2 Mithral Breastplate, 8 AC: 8,200 gp

It will cost you 575 gp more to sell your +1 chain shirt and buy a mithral breastplate than to upgrade your existing shirt to a +2.

So if you want to stop at 6 AC (and no special abilities) then upgrading the shirt is the way to go.

If you want magic abilities or more than 6 AC, you'll want to invest in the Breastplate.

Math:
Upgrading an existing +1 Chain Shirt to a +2 Chain shirt costs you 3,000 gp resulting in 6 AC.

Selling the shirt (625 gp) and buying a Mithral BP costs you 3,575 gp, also resulting in 6 AC.

Upgrading a +1 Chain shirt to +3 Chain shirt costs 8,000 gp.

Selling the shirt and buying a +1 Mithral BP costs you 4,575, far cheaper than the shirt for the same AC. And it continues like that the more you enchant it.

[Lab_Rat]

Also...the armor expert trait is great with the mithral breastplate. Makes the armor check penalty 0.

I vote for ditching the chain and grabbing the mithral breastplate.

[Jiggy]

If you plan to ever get your total armor bonus to AC up past +6 in light armor, you should be using a mithral breastplate.

At an armor bonus of exactly +6, a mithral breastplate and a +2 chain shirt are the same bonus for about the same price (both are 4k and change).

To increase it by 1, the chain shirt will cost you another 5k, while the mithral breastplate will only cost you 1k. The gap only widens from there.

[Erosthenes]

Thanks! I am convinced! Appreciate the help-very much.

[Seranov]

Additionally, breastplates are cooler looking.

This is of dire importance.