You need to look at your current window and figure out how much of the window cutout you can use for your new bi fold french doors.
Turn a window into a french door.
Also measure the window s location on the wall compared to where you will place your door.
The good news about turning a window into a door assuming it s wide enough is that the advanced carpentry required for altering a load bearing wall.
Dan faires explains why it s better to let a professional install french doors.
So you ve just built a new deck on the back of your house and those once lovely double windows in the living room would now make a better door sliding glass or french out to that awesome deck.
Here is a recent response on cost to install a sliding glass door which is quite a bit easier than a french door but same general size.
Installing a french door between a living and dining space creates privacy without the loss of an open feeling for example.
Because you are almost certainly going to be increasing the width of the opening and very likely raising and lengthening the support header over the window as well you are going to to be above the cost in the referenced comments probably in the 2000.