To how many odd keystones can one Spiritomb be synchronized?

Spiritombs have the "Keystone Warp" capability, which says the following:

Spiritomb carries around with it an Odd Keystone. Trainers may collect additional Odd Keystones as they travel. They may then synchronize them with a Spiritomb for the cost of 2 Tutor Points. A Spiritomb may then freely teleport between any Odd Keystones within 10 meters as a Standard Action.

Do these 2 tutor points need to be paid for each individual Odd Keystone? Or is this a total price that allows a trainer to synchronize any amount of Odd Keystones that they have managed to gather with their Spiritomb?