In my experience fans from manufacturers like Arctic can be almost as quiet similar Noctua, but cost 50% less. The difference definitely isn't vast for most models, although admittedly there's more QC issues and variation than with Noctua.

A lot of Noctua sales come from their brand value. People put Noctua fans into their gaming PC's, use headphones while gaming on them, and then turn off the PC. You don't really need the most silent fan for that, but people buy them anyway for the looks & premium quality.

I do love Noctua's coolers though, I appreciate the well thought design, manuals and free upgrade kits when you upgrade your system to a new socket type. But for case fans I'll jut buy Arctic and save money, except for things like server systems that run 24/7 in my bedroom where noise and durability are top priority.