I have just come back from a kitchen experiment.

I added water to an insulated cup of ice, stirred it, waited a minute and took the temperature. 0.5°C, about 33 in those antique numbers.

I added a big whack of salt, stirred again vigorously to dissolve some and measured -2.6°C. I don’t care what that is in non-science units. If you like I can however convert it to Kelvin.

I’m sure I can go colder by using a proper salt solution (heat it to dissolve as much salt as I can) and crushed ice, not cubes, to increase the surface area. I’m guessing I can possibly get to -17° if I try hard enough. Just a hunch.