I work mon-fri, exercise almost every day so feel a night out once a week isnt exactly a big thing - Certainly not like university years of going out 5 or 6 nights a week. Stuff like stag do's and weddings will not continue forever either, im just at that age.
Regarding the time, it depends what the night is. A lot of club nights dont open until 11pm or even midnight. Hamburg, some of the clubs didn't open until 5am! (5-10)
Taxi wise I never spend much as am in the centre, think the most I have spend was £40 from York to Leeds when I missed the last train.