Bought a #1 X-Acto knife ($3.99 CDN), and a package of 5 #11 blades. To keep the pieces together, I printed a small container with the handle as the "lid". When storing the knife, remove the blade, place it in the container (backwards so you know which blade is in use), and slide the handle through to close the container. Very simple in Openscad. (attached)
OpenScad - outside cube, subtract cylinder and inner cube. Fudge factor to make it slide in easily.
translate([-31,0,4+(fudge/2)]) rotate([0,90,0,]) cylinder(d=8+fudge,h=62);