I’m a big fan of Zara’s denim (its jeans are way more long-lasting than you might think), and the Black Friday sale traditionally cuts prices to less than £20 for some staple styles.
They come in 18 different washes, so there’s a pair for you, whether you like traditional denim washes, white, black ... If you prefer high-rise jeans, the Zara TRF High Rise Wide Leg Jeans ...