Sorry - not sure what you are trying to prove !
If I know EXACTLY which geberit cistern I want them yes I can online search and get the cheapest .
Using your duff logic - I’ll just buy any freestanding bath ( as long as it’s the cheapest ) , any rimless toilet ( cheapest of course - even though YOU said rimless was pointless ) , any kitchen ( cheapest ) , any front door ( cheapest ) etc. Etc. Etc .
YOU want cheapest ! I don’t ! . But that doesn’t mean I want most expensive!!! ; as there is no upper limit for these things .
i am willing to pay more than “cheapest similar “ - that’s all .
The savings on my build were because of my efficiency and work - finishes in my opinion are subjective and should suit the value of the property. Would a 1 million pound house be ok with a 5k kitchen ? . Of course it would ; it’s just as functional. But when you try to sell it - that would pop up as an issue...