a VirtualTourist member
Is it more expensive to collect and return car at the airport?
If you consider travelling from your hotel to airport with luggage, renting a car in the airport saves you time and transportation money. I don't think the rates change dramatically, but they could be a bit more than renting in the city.
Interesting question - I've just checked Budget Rental Car and their cheapest car is a Hyundai Getz. One day base rental is 30.20 at both city and Melbourne Airport but is 37.00 including fees at city (Franklin Street) and 43.00 including fees at airport.
By shopping around you'd get a better deal and the above is just one of the companies.
As noted above if you are intending to rent a car, the return to the airport in the rental car does make sense depending on where you are coming from.