My question is the exact opposite of this one. I'm considering getting a sous vide tool like this one. I'm wondering what's preventing me to use it as a slow cooker?  Like, would it make sense to use the sous vide thing to circulate water in a bain-marie, and cook something inside a second bowl? Maybe that's overkill, or consume an unreasonable amount of energy?  If that's not a good idea, what's the cheapest way of getting equipment that allows you to do both slow cooking and sous vide? 
I think its possible, but because you can't fit a lid on top of whatever pot is holding the water (well, not easily; you can do some cutting to make a hole for the sous vide device in a plastic lid, but then that lid/pot become dedicated to the technique), and that lets the heat escape probably more than what would be desirable for what you're trying to do.  What you really need is something more like this.  It controls the water temp to perform the function of an immersion circulator for sous vide cooking, but it can also be used for slow cooking without the water.  I searched Amazon for sous vide slow cooker and got lots of results. 