Which species are you looking for? Polypterus senegalus is the most commonly available along with Polypterus ornatipinnis and P. endlicheri endlicheri.
Polpyterids/bichirs are a grey area speceies since they can't be imported you are denpendant on captive bred specimens.Polypterus senegalsus can go for $100-$200 AUS prices can rise dramaticly from there.I have heard of very few P.delhezis for sale in Aus-Anne