and with the boxes insulation compromised, how long does that ice last? Ice in supermarkets around here isn't that cheap. Would be interesting to see how the costs of making the ice yourself would workout, if you were constantly having to run the freezers compressor to make ice.
I'd personally just spend the extra and buy the airconditioner. If air conditioning is a requirement, then i would not want to leave it upto a hit and miss device. Once instant where you don't top up the ice because you're away, or you forget, or have no ice, and it could fuck your grow. At least with an actual AC unit you have the peace of mind knowing it will just keep on doing it's thing and keeping your plants happy.