Mini buses are the cheaper option.
The airport is in the north of the island and your hotel is in the south - at least an hour's drive by car, more if its in heavy traffic.
By my calculations at B900 the taxi cost is still only about $35AUD, so its still about one third of the cost of an equivalent taxi trip in WA. Keep this in mind when you are considering other options which may take longer and not involve door to door delivery.
There are also private drivers which do not only day tours but also reliable airport/hotel pickups.