Takes about a week, cheap and very easy. A decent kimchi here is £4.50 for a small pot, maybe 250-400g? I can make 2kg+ for less. Kimchi is the only one I've seen sold out of the list too. I highly recommend trying it, if you have a vac sealer it's even easier.
But, yeah, you don't really save money in general and decent commercial products you can easily get many places are as good or better.
There are exceptions. Some bread products (including biscuits etc.) are reasonable to make at home, especially if you don't have convenient access to a good baker. (There are a few in the city but not near me.)
I find cooking in general is rewarding and can save quite a bit of money.
Kombucha is the exception.
I make kombucha at home. The labor is extremely minimal (basically the same effort as making a gallon of sweet iced tea) and the economics absolutely make sense - the cost less than $1 a gallon for me to make it vs $3-5 for 16 oz at the grocery store. Plus I already have pounds of tea at home.
The other reasons I make it are to avoid having to haul heavy bottles into the house and because I prefer unflavored kombucha and only flavored ones are widely available commercially.
Yeah, if you use a lot and are just producing unflavored, kombucha is pretty easy/cheap.
But its a fun hobby - if you can stand the long feedback cycles.
Personally I'm pretty much only making a sort-of curd-cheese now [1] with left over (sour) milk. Its fast to make, only ages for a couple weeks, and then I use it in a quiche. Which works really well and us more of a way to use excess milk than actually "make cheese".
[1] I use citric acid and heat to separate the curd, then put that in moulds to drain for 2 weeks are do - minimal pressing. Forms a firm, crumbly curd with a mild sour flavor.
I made a large wheel once, and matured it for a year, and it was edible, but nothing special. That's too long for me to get the feedback I need to improve.