Echo terenz
http://www.bayswatercarrental.com.au/
Cheap, good cars. For the extra couple of bucks I would get a new one.
Can get pricey if it involves a lot of miles in a short number of days.
Short taxi ride from the airport, or your friend can catch the train to Kings Cross and its a few blocks away. (Not to be recommended much past dark , particularly if you have luggage).