Just out of curiosity I sought a quote on 2 days car rental from Tullamarine and got $115.
That would run $90 after discount for 2 days (cheaper than cab each way!) and includes:
Rate Inclusions
The total price is inclusive of the following:
Goods & Service Tax
State Tax
Third Party Cover
Stamp Duty and Administration Fee
Unlimited Mileage
Vehicle Registration Recovery Fee
Premium Location Fee
One Way rental fee (if applicable)
Most attractive deal I thought at $45 a day all in.