Custom Magic Item Creation
Following Magic Item Creation Rules, this would be pretty simple and straight forward.
How I Would Do It (Opinion)
Let's break it down.
Base Cost: From the first entry under Spell Effect (Command word), we can see that the base cost should be Spell level x Caster level x 1,800 gp.
Modifications: For a tattoo like the one you mentioned, it would be a slot-less item, which adds the "No Space Limitation" modification, which doubles the price. And, as you suggested, using X times per day, you divide by (5/X), where the higher value for X results in a higher price. This second modification is taken from the "Charges Per Day" row under Special.