Choices for accommodation around the University of Sydney can be found on the University web pages. Here are links to budget accommodation and to standard accommodation. Scroll down in each case for details of location and prices.
Details of location are often hard to judge for those not familiar with the area. The University of Sydney is visible on Google Maps here. Plugging in the address of possible accommodation sites to Google Maps will show you clearly where they are in reference to the University. For reference, Central railway station is the bit with the spaghetti of railway lines visible, and the distance from Central to U Syd is about a 15 minute walk. This might help to give you a rough indication of how far away different accommodation is from the University.