We were in Gladstone for a friends wedding and shelled out a couple of hundred dollars to fly in and out from Brisbane. The plane was only little (seated around 100 I guess) but it was much better than driving up.
We flew Qantas Link and I am sure you can get heaps cheaper tickets if you are not tied down to a particular date. The flight was pleasant and only the waiting around before the flight was boring.
We were staying in Goondoon St and really saw everything we needed on foot or using the taxis. For any longer of a visit definitely hire a car.
The taxis were just called Gladstone Taxis and they were very friendly and very prompt when called.