Kimchi should be stored in the fridge as chilling is the only thing that keeps its level of fermentation (i.e. the activity of those happy little probiotics) slowed down. If you leave kimchi outside of the fridge, over time it will become over-fermented and won't taste so great anymore.
A typical 15-ounce jar of kimchi costs about $8.99, which is about 60 cents per serving. However, if you make a gallon at home, your cost is about $15.66 and averages out to 12 cents a serving [source: The Kitchn].