We have done this, or at least are in the process of doing it with the 12 doors in our bungalow.
We have collected doors from neighbours (who have been disposing of them), and from freecycle. We have also collected original bakelite handles for all the doors
This door (like all the rest) was painted, so we had it dipped. We carefully removed the top panel with a multi tool, and the local glaziers made a glass panel for it, which we asked them to sandblast. We rubbed the door down and waxed it, before putting in the glass panel.
The latch and handle were in a different place, so that all had to be chiselled out (and the old hole filled). Also the door was a different size to the frame, so some adjustments were needed there.
It was a time consuming process, but we are delighted with the end result. (Only another 6 to do now!)
Total cost was about £60 per door (for dipping and the new glass panel)
Fortunately my DH is very handy, and I am a willing labourer.
If you don't have good DIY skills, I guess it would be considerably more expensive if you have to pay a joiner (or carpenter?) to fit it.
Hopefully the photo is attached... (my first attempt to do so!)