Advice relating to the value of a homebrew item.

[Barathos]

Helm of Invisibility (wondrous item, head slot)

Lowering the face-guard of the helmet causes it to turn the wearer invisible as though Invisibility had been cast on you. 3 minute duration, 1 use per day. Requires one free-hand to activate.

How much should this item cost?

[Bob Bob Bob]

Simple answer? Price it like 1/day invisibility. Command word, Spell Level x Caster Level x 1800 / (5/1). 2,160 gp. Lowering the face guard is a standard action, simple "cast X spell Y times a day" item.

If you want manipulating the helmet to be a free action you probably have to price it like 1/day quickened invisibility (which would actually be a swift action) raising the SL to 6 and the CL to 11. This would increase the duration to 11 minutes, but it'd also multiply the price by 11. So stick to the first one.

[Barathos]

@Bob Bob Bob

Thank you.