Yep, Customs are without doubt a bunch of scammer, thieving $^%&*#&^@#^(*
After you hit the $1000AUD value, you get hit with 5% Duty (calculated on the $1000 plus a VOTY figure that Customs magically come up with), then 10% GST (on the value + the Duty), plus the Customs paperwork fee, and if the item is 2nd hand you'll also wear the AQIS inspection fee (huge)....plus the freight operator's charges etc.
Trick would be to get your US supplier to split the invoice, and freight the item in two consignments if possible......keep the costs below $1000AUD on each consignment.