This is exactly the point.
Twenty or thirty years ago, everybody had a watch. You needed one if you wanted to know what the time was.
Today, that role is taken by your phone.
Watches, have gone from being a practical piece of equipment that most people needed to what is, essentially, just a piece of jewellery.
A cheap watch in the past has been replaced by a cheap mobile phone today (which typically starts from around £50 at Tesco etc).
So when people are talking about "cheap" are you talking about watches as a functional piece of equipment to tell the time or are you talking about items of jewellery?
Your answer to that question will likely determine if you think that £400 is expensive for a watch or not.
For context, the last time I bought a watch (which I still have but don't wear very often) was about 15 years ago and I think it cost me less than £100.
My DH does have a brand of watch that has been mentioned earlier in this thread, that he also bought around the same time, and paid around £5k for it. Today, it appears to be worth slightly more than that.