Crock pots can be hacked fairly cheap to work. This is one way Sous Vide Cooker for Less Than $40: 7 Steps (with Pictures)
But Sous Vide devises are so cheap now. This is one that I tested for my YouTube channel. Temp control is not as perfect as I like but still works good. https://www.amazon.com/dp/B01MT79EQD Its only $80 and relatively small.
Nice.
I have an Inkbird external thermostat. It was about 20 bucks and I use it for brewing. My problem is that money is tight right now and if I had an extra $70 or $80 it would be for an immersion blender. Sous vide is maybe second or third on my list unless I can hack an oven or a crock pot.