What price guidelines for arbitrary concentration check bonuses in PF?

[gomipile]

If I wanted to add magic items of various bonuses to concentration checks to a Pathfinder campaign, what price guidelines would be appropriate? Would it be appropriate to simply use the skill bonus guidelines, since concentration was a skill in 3.5? Or, should the price be different because concentration works differently in Pathfinder?

In any case, my gut feeling is that it should be significantly cheaper than an ability bonus.

[Der_DWSage]

According to the one item (http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/r-z/tunic-of-careful-casting) I've found that gives a bonus to concentration checks, it seems that the bonus is either 2500 GP per +1 bonus to Concentration, or some odd formula that I don't care enough to reverse-engineer. Either way, definitely more than a skill bonus, but less than an ability bonus.

[Firechanter]

Check out Spellguard Bracers and the Tunic of Careful Casting. Both add +2 for Defensive Casting checks, plus some other boons, and cost 5k each.

[Ilorin Lorati]

Judging from the prices provided by the items already shown by others, and the general pricing guidelines for magic items, I'd say the purchase price is probably "the item's bonus squared x 1250gp" for a flat untyped concentration bonus.

A concentration check bonus merely for casting defensively either is considerably cheaper or the reroll provided by Spellguard Bracers is dirt cheap.