Above the lowest levels, it's seldom worth giving up an action to take a CLW. I'd guess this item will usually not be used during combat.
For items with instantaneous effect that are mostly used outside combat, I charge as for a slotless item. When not marking rounds, it takes trivial time to swap one item for another; the character could carry a dozen Circlets Of Healing and get nearly the full benefit from all of them.
So I'd use kreynolds's price, and double it for slotlessness. Then I'd probably round down, because the item is slightly less flexible than a truly slotless one, and because I like multiples of one thousand.
Call it 2000 gp even.