There are many options for staying in Melbourne.
Melbourne International Backpackers has been the official backpacker of every Melbourne Noctis event and has never disappointed. It is located at 450 Elizabeth St, Melbourne.
HotelClub allows for searched over many hotels in the area. Any hotel easily accessable via public transport (trams especially) would be suitable, though one close to the city centre would of course be ideal.
If you leaving it to the last minute, wotif.com may be able to help. Wotif provides last minute special for hotels up to 28 days in advance, so you will need to wait until at least the end of March to make use of it.
Jenny has volunteered to organise billeting for those wishing to save money, so email her if you need billeting, or if you wish to volunteer crash space for others.