I agree, it is no one's business who much I spend on my bike or bike accessories or bike trips. I can pay my bills and give to charity...so I can afford it.
I chose to spend $$ on these healthy pursuits than others.

As for how much one is willing to spend. Really an individual question.
What is your budget. How much will you ride. How serious are you about this?

Starting out it is best to fine an entry level bike that fits you! Then I think one can move "up" in the world (although some people do not feel that way).

I moved to a all carbon bike a year ago. That was after many moons, trips and miles on my current aluminum steed. I knew about how much I could and would splurge. And I love every penny I spent. So it is all about what you can afford and you are comfortable parting with.

I know many people whose first bike had to be at a much higher level than their experience. But they felt they could afford it. (and maybe they could--who I am to judge) As long as they don't let it sit and gather dust!