Doors have a surcharge as they need extra battens to space the shutters away from the large door handles, plus the frames normally need cutouts around the skirting board.
The number of shutters, how they fold or louvre size will not affect the cost, it’s just based on the width and height of your door.
Shutters on doors are fitted within a 3 or 4 sided frame, like a door would be. This frame is fitted onto wooden battens for added strength and so the louvres miss the door handle. Depending on the style of your door and the number of shutters you don’t have to have a bottom frame.
They are fitting inside the recess and finished to the wall with a shadow gap rather than using filler to neatly blend the two surfaces together.
Where possible, the number of shutters should match the door, they could be large single panels or split into 2 shutters so they are hinged in the centre and bi-folded.
A bi-fold will take up less space when the shutters are open which can be an advantage if the door is used a lot.
With just 2 large shutters opening left and right, you don’t have to have a bottom frame on a door shutter, this avoids any trip hazards. However, you will need a bottom frame with 4 bi-folding shutters, unless you choose to void the guarantee.
If your door height is over 2m will need a horizontal rail in the shutter for strength unless you upgrade to the Elite Plus shutter. This is a thicker and stronger shutter can be made without a rail in heights up to about 2.2m, I would recommend this if you have just glass in your door running from top to bottom with no break or divisions, you don’t really want a rail in the shutter if there are no rails in the door.
Without a rail, you would need to split the louvres as doors are too high for the louvres to all be tilted in one go. This option allows you to open the louvres independently either side of the split, a popular option if you have pets.