I bought a cheap pair of Regatta trousers from Mountain Warehouse, waterproof,breathable and with taped seams for under £20. Good enough to pass kit check and if you ever had to wear them they'd do a decent job, although not brilliant to run long distances as you tend to sweat a lot in them but there ok. There is a lot better quality on the market but not at that price.
I'm sure someones gonna come on here saying you should never skimp of waterproof safety gear and I agree if its not gonna work, and would never purchase an equivalent jacket from Regatta but these bottoms are pretty good, I've ran the fells in pretty bleak weather in them and they was not bad.