I see that a post sneaked past our normally ever-dilligent moderators 
I'm a huge lover of kefir (I know many people hate it). I used to buy it in 1L cartons for about £1.50.
These gradually moved to the 'ethinic (Polish) foods' section, hidden away as smaller 'boutique' versions arrived.
Eventually the proper Polish stuff disappeared, and even plain kefir is only available for about £1.50 for 200ml in a plastic bottle.
Tip 1 – take a small amount, add it to 4 pints of full cream milk, leave at room temperature for 4-5 days.
Tip 2 – don't use semi-skimmed milk by mistake, it ferments, but it is not the same.
Neil