Yeah it includes everything including a specialist surveyor who makes sure they're millimetre perfect. I would do it myself if I could find a UK company that does them - found a shit load in America, you can get them in fucking Walmart over there cut to the size you want but not here it seems, yet at least.
I just Googled this.."Arched window blinds uk to buy online" and at least a dozen appeared.
Most of them will appear just because of the key words in your search. Once you go in to more detail they're hard to find, if you can find me a site that shows a perfect arch that I can put measurements in and order then be my guest - you'd be better at Google than me.
Maybe I don't trust you foreigners Nah, doing it myself is the last resort because of how awkward it'd be, I'm more than willing to pay a price that I'd consider fair - I knew they were expensive which is why I set aside around a grand specifically for it but any more than that is just extortionate.