The CoolBot “turns any brand of off-the-shelf, window-type air conditioning unit (purchased separately) into a turbo-charged cooling machine. With it, you can transform a highly-insulated room into a walk-in cooler, keeping your vegetables fresh and thermostatically controlled cool down to 32° F!” And it’s only $300. Combined with a $300-500 air conditioner, CoolBot promises to deliver the performance of a commercial cooler compressor that would cost at least $3,000. It also saves around 60% on electricity bills. Installation is incredibly easy: tape a CoolBot sensor to the A/C unit’s temperature sensor.
For building a low-cost walk-in cooler, here are two articles that take entirely different approaches. Both are well worth the read: