lots of fun techniques, a common one for getting down low enough where other methods become practical is stirling cryocoolers, and those are even on ebay for a few thousand (cascade refrigeration systems, and joule thompson coolers, and a few others are also used), way down past that theres stuff like weird magnetic coolers, and dilution coolers All very interesting, reading about exotic cooling methods is quite fun.
It sounds like a lot of the precursors are too generally used to blanket ban them because of fentanyl. Kinda seems like this is just the cost of seamless worldwide shipping, we simply can’t open every bag of cat food being shipped to make sure its not a fentanyl precursor.