Do rods, staves, and wands use up a magic item slot for a character?
If they are slotless items than the cost of inscribing a magical tattoo version of one of these items should be the same as creating the item through the normal feat.
Magical tattoos are treated as slotless magical items for pricing purposes.
I believe the inscribe tattoo feat specifies that the tattoos follow the rules for wondrous items, so no magic stick tattoos.
Rods, staves, and wands must be held, in order to be used. Tattoos don't need to be "held" in order to be used.
To me, it seems that magical tattoos are allowed to mimic metamagic rods, as the Caster's Tattoo, made with Inscribe Magical Tattoo, allows the use of Still and Silent metamagic with spell casting.