wow thats a big question to answer. I mean (at johns - practically the same as bruce anyway - despite what neo_o thinks) there are people who are living off government benifits, or having to work (12+hrs a week) themselves to pay for the fees, and anything else they might incur. On the other hand there are people who are given "daddy's credit card" and can go loose, provided its justified.
In my case - Mum&Dad pay for johns - i pay for everything else (beer, shampoo, field trips, text books etc lol )
At the end of the day all you really spend money on is beer, party related things (i.e. theme nights), snacks, text books, field trips, tolietries/washing powder and the odd thing here and there, and nights out with people (i.e. bday dinners) [oo and gf]. first 3 weeks is probably the most expensive, after that you could easily spend less than $30 a week.
If you've got to propose an amount to our olds - get them to cover bruce, text books, field trips etc. then start bargaining from there.