The charges are probably correct and reasonable. You are lucky you did not get slugged for more. My advice to all importers is;
1. Ask the supplier to quote the goods on the basis of FOB or EXW. These are the incoterms. In your case they quoted DAT. I urge you not to get DAT unless you are an experienced importer. there is not much upside for the buyer!
2.get a quote from an Australian Freight agent/broker/forwarder, based on FOB or EXW