It depends on what you're planning to do with these notes.

For me notebooks go straight to paper recycling after a while, the space and burden is just too much. Anything I intend to last any devent amount of time is digitized, and scanning notebooks is a PITA.

Sure. But most of my notes are lecture slides as PDFs, and I have e-books also as PDFs. It's much easier to annotate directly on a PDF than to have to print them, annotate, scan, and ensure the scan quality is good.

At some point, 'it's cheaper' is just not a good enough argument for paper notebooks versus the sheer versatility of an iPad.

I would have to buy a veritable cart-load of writing stationery to emulate everything I do on my iPad. It would likely still be cheaper, yes, but it would also be much more of a pain in the neck.

Except at some point those books end up in some storage box in the basement, or potentially tossed out. Digital notes are forever with iCloud/Dropbox/etc and can be searched anytime.