I've had quotes from £1,800 for a composite door (Solidor) to £7,000 for a designer timber door (London Door Co). It is literally a door. No side windows or anything. It's a mid-terrace house, 1920s, nothing special.
I despair. The cheaper door isn't even especially nice. I've looked on eBay out of desperation but there's only one door that's the right size and that's far too modern for our tastes.
Keeping our current door is not an option as it's falling apart.