i pay £50 a month as i buy my own food, do my own washing, pay for internet and use my mobile for phone calls. otherwise it would be £100. although i do try to treat them to things etc. especially my mum as she does a lot for me.
i think my rent would probably be higher though if my mum and dad still had to pay for a mortgage.
(I'm 23)
edit: I did move out a couple of years ago so i know the rough cost of bills etc in "the real world" however, i split with my bf so had to move back home due to the salary i was on at the time. im saving to move out now and i get the impression my parents want me to move out soon so they can move and buy a smaller place.
my mum is very reluctant about taking money so i try to give it in other ways so she wont notice