Depends on usage and whether a diyer or semi pro.
Either way i wouldnt go mister absolutely useless for above basic lathe work, generally ok in limited fashion for milling.
I have a fair few tools that wont work without coolant and also quite a few with through coolant a mister cannot supply or manually get at.
The aim is to keep job and or cutter cool and provide a little lubrication, cutters last longer and should get a better finish. Misters for me dont provide enough cooling, in no time developing steam but far better than running dry.
My main tanks running a bit weak now not long finished off 25ltrs of Castrol about 18 months to two years, need to get some more or an alternative.
Not keen on the synthetic to me it just dont look right opaque water but does a good job. Previously used rooks of Listers, loads of Morris types and many from Smith and Allen the last 8 years. Out of all used there was only one type that stank due to being left a couple of weeks mid summer.
Worth mentioning one small tank usually have to top up through evaportion 1-2 ltrs a day in summer, winter 1 ltr about every two weeks.
If really tight, make your own.
Any oil will do along with a detergent. If had to buy even the cheapest oil it will work out dearer than buying ready mixed delivered to your door – pointless.