I have an old Crock Pot slow cooker that has one setting: on. Modern ones have two or three temps, a timer and maybe a probe. I have not seen any with (continuously) adjustable temperatures (e.g. a knob). True, adding a thermostat makes the under $40 price point harder to make. But it would seem that there is a market for slow cookers with a temperature range and a probe. Tefal has a tagine with an adjustable temp.
Is it just price or is there another reason these things don't exist or are hard to find? (Oh, and yes I know I can add a temp control as part of a "make your slow cooker a sous vide cooker" -- but I don't want to :).
(Edited for clarity.)