Well before paperbacks became the norm every publisher (or it seems like every publisher) had their own “Pocket Books”. Produced with differing quality and obviously different prices, though I am not convinced that any were of a low enough price to reach a massive audience.
Elizabeth Taylor famously bought Richard Burton a set of Everyman, knocking on for a thousand books. The choice of “Oxford World Classic” titles I suspect was influenced by a degree of nepotism, though that shouldn’t be surprising as “Oxbridge” thrives and is built on nepotism.
I am particularly drawn to the “Nelson” blue faux leather series. I have well over a thousand titles though from various publishers and some very “attractive” sets, nearly all are well bound and some have very striking dust jackets.