some updates:
By to days prices a beer in a pub, usually 0.5 litres, will cost you an 70kr, which is about 7 GBP or 10 USD. In the Vinmonopolet a bottle of vodka will relieve you of about 50 USD or 35 GBP, when a bottle of wine will cost about 10 GBP or 15 USD.
If you go to a small city or to Trondheim there will be practically no problems with the bouncers. They are strict if you show unapropriate behavior towards other people or staff but will tolerate quite an amount of drunkedness before throwing you out. Drunk people buys more drinks than sober people. One of the regular punishments if a bouncer sees you as unfit to come into the club is that you have to "walk the round" which would then mean that you have to take a good walk before coming back. Then they most likely wont remember you and if your not too obviously drunk you will get in.
Also the age limit in a pub/club is the same as in the store, and that is that as an 18 year old person you can buy drinks with up to 21% alcohol(beer, wine, winecooler, ciders, some shots etc.). Anything above that is limited to people over the age of 20.
An ordinary beer from a store will cost you about 2 GBP per 0.5 litre or 3 USD, 20 kr.
So one get quite tipsy on the vorspiel before going out and then finishing the night off with some expensive pints at a pub or a club and a nachspiel. These nachspiels usually lasts until the morning after. If its a good one you wont be back home until 8 or 9 am, or else you would probably be back arround 4 am because most pubs and clubs shuts down at 3 am.
One of the reasons one gets home late is the famous kebab. You can't go out drinking and not buy a kebab in norway. Thats tradition. A kebab at the first kebab store one see after leaving the club/pub have to be visited and merchandise bought(if your not bringing a girl/guy back home that is, then you would be excused).
A quick summary of a normal night out: Vorspiel from 7pm to midnight, pub from midnight until one, a club until 3am and then kebab, and then a nachspiel from 4am and until 5am - ∞(but would not stay to its more than 8ish - 9ish because by then people would probably be tired.
Come to norway!