UPDATED: NOVEMBER 10TH 2018
Most bars in Liverpool you can walk straight in without paying on the door. Saying that, some Liverpool bars do add a £2-£5 door charge after a certain time, so if you're on a budget, put at least £10 aside for admissions if you plan on staying around the bars in Liverpool. But generally, most bars in Liverpool are free entry.
And for those visiting Liverpool's pubs — I've never had to pay an entry fee into any pub in Liverpool besides on Christmas, and that was just to keep the doormen happy.
Regarding the admission costs for nightclubs in Liverpool, you'll pay no more than a £10 entry fee on a Friday or Saturday night — and that's in the minority. Though beware! This will increase to around £15/£20 if the club has a special event on with guest Djs.
Generally, the more trendy the club, the more you can expect to pay. But overall, £10 is the ball mark.
Let's say you visit Liverpool on Saturday night (Liverpool's best night out) then you head to a few bars, maybe a pub or two depending on your age, then you finish off at one of Liverpool's nightclubs, it's safe to say, £20 give or take £5 should cover your admission costs for the full night. Keep this separate from your main drinking money as not all venues accept bank cards — cash is always the winner on the door.