Anecdotally, UK, the cheapest yoghurt (believe me, I have researched!) just dropped from £1.10/l to about £0.7/l - anomalous considering the rampant groceries inflation we have, but there it is.
Milk is about £0.64/l, so roughly equivalent if you add in the cost of heating it.
However, the price for live yoghurt is a different story - much more expensive, which is why I have recently started making my own.
I don't think these kinda of comparisons are valid.
The cheapest yoghurts have all a very bad taste and consistency in the mouth while those you will do at home taste on par with those you pay a premium for.
Ordinary, but skimmed milk - mumsnet says you need to boil it for ~10 mins and then let it cool to ~40C before adding the live yoghurt culture. Working well so far!
UHT is usable, and doesn't need to be boiled, but for that added convenience it costs nearly twice as much.
Fresh milk is currently £1.45 for 2.27 litres, down from £1.65 at peak.
Tip for UK readers: You can put an unopened 4pt plastic milk bottle in the freezer and it will keep as long as UHT. Defrosts in a few days in a fridge. (Was handy during COVID lockdowns)
Milk is about £0.64/l, so roughly equivalent if you add in the cost of heating it.
However, the price for live yoghurt is a different story - much more expensive, which is why I have recently started making my own.