The cost of an arborist report will vary depending on exactly what is being reported on, the number of trees , and the nature of the application. Applications to council for DA approval are a little more indepth and will cost more to write up. Make sure you choose an arborist who is of the same thinking as you when they are writing the report. Quiz them on their thoughts before they begin. Don't pay $450 for a report that says you need to retain the tree if your objective is to remove it. https://www.gotreequotes.com.au/arborist-reports/