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.
Turning windows into french doors cost.
You can expect an average cost of 525 and up.
The cost to install french doors starts at about 400 and with labor estimates running between 75 and 180 per door.
Not only do you have to manage securing permits and the window company but you may also have to hire additional trades like drywall installers painters or electricians if you want the work to look seamless.
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.
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.
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.
The patio door after it has been installed.
They can be purchased at big box stores like home depot and typically range in cost from about 1 500 to 3 500.