Open door from inside or outside

Hi,

My dad has a Mazda 6 and recently the driver's door locked itself. It now won't open from the inside or the outside. All the other doors are fine. They will open, close and lock. He took the car to a Mazda dealership who has quoted £400 without labour. I have noticed in various chat rooms that this is quite a common problem with this particular make of car.

We were wondering whether there was any way we could fix this ourselves or weather you recommend taking it to an expert.

Thank you for your time.