I'm in my early 30s now so I've mellowed out a lot (a Friday night in with a takeaway and a movie honestly appeals to me more now than going out, drinking until 3am and waking up somewhere strange). In my 20s though, anywhere from £50-100 was normal. Shit adds up quickly. Taxi to someone's house, a few cans of drink from the shop while we're there, cab in to town, a few pints in a pub, pay to get in to a club, more drinks, pay to get in to a second club because the first one was dead, more drinks, drinks for other people, more drinks for myself, kebab, taxi home. Rinse, repeat.