An Australian One Dollar note (Phillips/Randall - serial APK), uncirculated and in absolute mint condition could fetch anything up to $85 AUD. If it has been circulated but still in good condition, it might fetch anything from $1 to $2 AUD.
A reputable coin dealer will be able to give a more accurate valuation.
This is the most common Australian $2 note, circulated examples are only worth their face value, if in Uncirculated condition they retail for up to $10 each.
$2,999
A Commonwealth of Australia Two Dollar note (Coombs/Randall)(serial FKD to FPS), uncirculated and in absolute mint condition could fetch up to $295 AUD. If it has been circulated but still in good condition, it might fetch anything from $40 to $110 AUD. A reputable coin dealer will be able to give a more accurate valuation.
A Commonwealth of Australia Ten Dollar note (Coombs/Wilson - serial SAA -SDR), uncirculated and in absolute mint condition could fetch up to $95 AUD. If it has been circulated but still in good condition, it might fetch anything from $15 to $35 AUD. A reputable coin dealer will be able to give a more accurate valuation.
A Commonwealth of Australia 1968 One Dollar note (Coombs/Randall)(serial AGE to AHY), uncirculated and in absolute mint condition could fetch up to $990 AUD. If it has been circulated but still in good condition, it might fetch anything from $80 to $390 AUD. A reputable coin dealer will be able to give a more accurate valuation.
Impossible to say without knowing the note's denomination.
A Commonwealth of Australia 1967 Twenty Dollar note (Coombs/Randall)(serial XBQ to XBS), uncirculated and in absolute mint condition could fetch up to $9,000 AUD. If it has been circulated but still in good condition, it might fetch anything from $500 to $2,600 AUD. A Commonwealth of Australia 1968 Twenty Dollar note (Phillips/Randall)(serial XBS to XEU), uncirculated and in absolute mint condition could fetch up to $425 AUD. If it has been circulated but still in good condition, it might fetch anything from $45 to $200 AUD. A reputable coin dealer will be able to give a more accurate valuation.
You could try a reputable coin dealer in your area. Check the Yellow Pages under Coin Dealers. Alternatively, if you know enough about banknotes to describe it accurately and value it, you could try eBay.
Modified coins have no collector value. It is worth One Dollar in Australia.
The Royal Mint has never issued a 5 Dollar coin for British use, much less one with a "5 Dollar" symbol on it. The British use the Pound and issue a "5 Pound" coin, but not in 1988. The coin is possibly from one of the 50 plus Commonwealth countries and should have the country name on it somewhere, most likely Australia, Canada or New Zealand.
Not enough information. Has it been circulated? Is there anything unique about it? Whose signature is on the front? What is the serial number? Notes printed from 1966-1972 will have "COMMONWEALTH OF AUSTRALIA" printed at the top, front and back. Notes printed from 1972-1994 will have only "AUSTRALIA" printed at the top, front and back.
A Commonwealth of Australia 1967 One Dollar note (Coombs/Wilson), uncirculated and in absolute mint condition could fetch up to $90 AUD. If it has been circulated but still in good condition, it might fetch anything from $10 to $32 AUD. A reputable coin dealer will be able to give a more accurate valuation.