Can you justify a few hundred for a big chest freezer and a cooler? Then you can use the cooler method described in this link or in one of the other comments from ir77 on this thread. But just put the cooler inside the big chest freezer.
It is also terribly slow. I was thinking about something like a cold plate on top of which there is pot of water with insulated sides that freezes from the bottom up - and something to move the water around. so you get constant remelt of the top layer so no impurities.
A second hand ice cream maker could provide the cooling power.
https://www.alcademics.com/2010/08/a-homemade-giant-crystal-...