Free online graph paper. Any size grid. Squares, rectangles, triangles, hexagons, and circles. You can even make paper for music notation, accounting ledgers, logarithms, caligraphy, and more.
Just tell it what kind of paper you want, specify the details, and in a matter of seconds it creates a pdf you can print out as many times as you want.
I haven’t bought graph paper since 2002.
The link’s here: http://incompetech.com/graphpaper/