Price is per 1 character. For example 4$ = 1 Char max Rarity - 12$ = 3 Chars max Rarity

Be sure to have enough Zeni to buy enough training materials for this service.

U need to have enough Dragon stones or Stamina recovery items.

This will include : Farming all medals needed to upgrade your card to max rarity. And using training materials + medals to upgrade your characters.