Cheap at half the price ... Utility knife plus 50 blades, $9.88.

One note on the various EDC knives mentioned with regard to cutting cardboard and blade geometry. Some hollow ground knives (such as the Dozier mentioned) make shallow cuts very nicely but as more of the blade is used the pressure stacks up because that narrow edge suddenly gets thicker. IMO a flat ground knife does better at slicing.

All that said, the utility knives mentioned use very thin blades that add very little pressure as they slice because the blade material itself is very thin, let alone the edge. For cardboard Id go with a generic utility knife every time.