10 quid a pint

That's either bathtub-sized batches (and all the work that means) or they're gouging. Rule of thumb if you can find it in supermarkets they're not brewing in bathtubs as supermarkets demand quite large minimum volumes.

Over here in Germany we have Störtebeker, they're not exactly a microbrewery but a (quite old, actually) small, independent, regional, brewery who for the longest time simply brewed their local Pils and maybe one or two other bog-standard things. Then they had a look at the market and came up with new recipes using all kinds of fancy methods and special yeasts and aroma hops and everything, leading to things like their Atlantic Ale, the missing link between Pils and IPA, for about 1.30€ per half litre bottle. That's about the same price range as big beer brands with TV ads, or a Budweiser (Czech of course).

Some pictures for a sense of scale. Sure that's way beyond the bathtub league but compared to actually big brewers it's tiny.

Occasionally they have actually expensive stuff but then you're looking at five times ice-distilled beer or such. Shouldn't be surprising that that's five times more expensive you're buying quite a bit less water.

If you want to brew at the bathtub scale, commercially, open a pub or probably better restaurant and do beer pairings.