Exactly this.
I am still picking my jaw up the floor from having to spend £2400 on blinds for two windows. This is what happens when you allow architects to design weirdly shaped/angled glass in your home. I thought the windows were expensive, but that’s before I found out the price of blinds to cover them.
Curtains are very expensive. The H&M Home options now look very appealing.
Lighting is crazy expensive. Let’s say you want 2 wall lights in bedrooms and bathrooms, that’s around £100 per light if you are thrifty and willing to do a lot of shopping on weird China-based websites (my tip: use Trustpilot. There are loads of fraudsters in that area). That’s not including the electrician, wiring and dimmer switches - or the bulbs, which also add up.
Ceiling pendants, if you want real quality you’re talking thousands per pendant. Even “cheap” knock offs will be mid-hundreds.
If you want led strip lighting, for instance on stairs, joinery, kitchen etc, that’s probably another grand or more if you want good quality, continuous (not little dots of light).
Joinery - we were quoted over £150k on joinery alone. That didn’t include the kitchen. And (sadly) we didn’t have anything gold plated. In the end I assembled a mishmash of ikea, DIY kitchens, bespoke doors from Superfront, Noremax, etc, and sourced door handles on Etsy, Amazon, and trade websites. I saved a lot but the time spent on coordinating all this is huge.
Decorators - I am in awe at people allocating 2k, we were quoted £34k (although our house is roughly twice the size of yours following extension). And I’m pretty sure that was labour only (didn’t include paint or wallpaper).
On wallpaper : nice, Designers Guild/Pierre Frey etc will set you back £1000-3000 per room in supply only, not including installation.