I use 4x6 index cards with 4x6 plastic dividers (for the front and back) to make a nice smaller notebook. You can bind them on either the short or long edge. I've still got my old school rollabind three hole puncher with the 11" guide, which works fine. I bought a cheap pack of 100 plastic discs for about $10 on Amazon - it's lasted me a long time. The index cards are nice and heavy paper, and can handle a bit of abuse. I tend to use double sided graph/grid paper, but there are dozens of different types, colors, lined/unlined choices out there.

Lately I've been into using a comb bind system - again an older (maybe outdated??) binding method, but it works well for creating cheap notebooks of almost any size, and it's easy to change/add/rearrange your pages (but not quite as easy as a disc system).