The best approach would be to breakdown all expenses to different categories; essential (housing, bills, fees etc.) and non-essential (travel, mobile, production costs etc). You can then present this to your supervisor and as a type of business plan for funding applications.
Take a look at the Postgraduate Research Handbook (ISBN: 0-333-74777-1) which should help you outline your research methodologies - once you've outlined these and discussed them with your supervisor you can estimate costs and contingencies.
Get yourself to your local postgraduate fair (there are plenty coming up in the next couple of months) for further advice. Also, any good university careers service will have a contact you could liaise with.
And finally, good luck and be positive