I like the bin the other commenter mentioned; using a case of frozen water bottles make great reuseable ice cubes too.

A chest freezer is a legit way as well since the cold mechanism is built in. Especially if you can find a good used one. If you go this route, I'd suggest looking into getting two things over time:

1. A pool liner to seal the inside better (you may or may not need this depending how water tight it is, though having that much water on the direct metal may corrode over time)
2. A temperature-regulated outlet plug - the freezer is going to always attempt to reach freezing, though you can bypass this by dropping the thermo dongle in the water and choosing your own temp. Another perk to this is, you can adjust it to precise temps and shift it over time.