I was using 1/round for activations. An unlimited-use command word activation item could presumably do this, and would cost 1.8 times as much as the trap (the time between auto-resetting trap activations is never defined in the rules, to my knowledge, so that's a bit of a grey area). One of the benefits of using food-generating items is space: without needing room for farming or livestock, you can house more people as your population grows exponentially (and you also don't need to defend the farms/livestock). The generated food can even be used to feed the monsters for XP farming.