How are these going to be printed? We used to have some notecards in various sizes for things like invitations at the printshop where I worked, but I don't know how well they would run in a desktop printer. For a pre-cut card like that you would also need to print on two sides of the sheet to have elements on every panel, or even on the front and one inside panel. It's also possible to print on lighter stock and fold a larger sheet, printed on one side, down to quarters to make a four-panel card.
Costs for printing will vary with the method and quantity.