This "mule" coin came about when the obverse of the Indian Quarter Anna coin and the reverse of the Australian Halfpenny were used together.
There is thought to be 10 or less of these coins in existence.
Both the Indian coin and the Australian coin were minted at the Calcutta Mint.
The rarest Australian Halfpenny is the 1916 (mule) coin, the 1923 coin is rare, and 1915, 1918 and 1939 (kangaroo reverse) coins are considered to be scarce.
The rarest Australian Halfpenny issued for general circulation would be the 1923 Halfpenny. It is thought that there were only 15,000 minted. One of these coins, even in poor condition, might fetch over $1,000 AUD. The rarest of all Australian Halfpennies is the 1916 "mule". It has the reverse of the Australian Halfpenny and the obverse of the Indian Quarter Anna coin struck on an Australian Halfpenny blank (or planchet). These are an error coin and should never have made it into circulation. It is thought that less 10 were struck and are worth tens of thousands of Dollars AUD. All known examples of this coin are accounted for.
An Australian 1936 bronze Halfpenny (George V), uncirculated and in absolute mint condition could fetch up to $225 AUD. If it has been circulated but still in good condition, it might fetch anything from $0.75 to $22 AUD.There were 5.577 million minted.An Australian 1936 bronze Halfpenny (George V)(Proof), uncirculated and in absolute mint condition could fetch up to $35,000 AUD.A reputable coin dealer will be able to give a more accurate valuation.
There is no Australian 1921 Halfpenny with a spurious "E" on it. You may have a genuine oddity. A reputable coin dealer will be able to assist with verification and give a valuation.
The Australian 1 cent coin was first issued in 1966 and last issued in 1990. See the link below to the Royal Australian Mint for mintage details.
Pictures of a specific coin are difficult to come by. Frequently you should be able to find one on eBay, but the picture is withdrawn after the coin is sold. The 1927 Australian Halfpenny is almost identical to the 1911 Halfpenny shown. The 1927 Australian Florin is almost identical to the 1911 Florin shown. See the links below.
An Australian Penny or Halfpenny with a "Y." (PENNY.) mintmark indicates that the coin was minted at the Perth Mint. An Australian Penny or Halfpenny with a "I" mintmark indicates that the coin was minted at either the Calcutta or Bombay Mints in India.
A set of first to last Australian Halfpennies not including the 1923 coin might get $80 to $100 AUD, maybe more, assuming they are in average condition or better. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coins. The 1923 Australian Halfpenny is the Halfpenny equivalent of the 1930 Australian Penny.
Halfpenny - British decimal coin - was created in 1971.
After the 1930 Penny, the Australian 1923 Halfpenny is the second rarest of Australian coins. An Australian 1923 Halfpenny, uncirculated and in absolute mint condition could fetch up to $60,000 AUD. If it has been rattling around in somebody's pocket but still in good condition, it might fetch up to $17,500 AUD. There were only 15,000 minted. A reputable coin dealer will be able to give a more accurate valuation.
An Australian 1923 bronze Halfpenny (George V), uncirculated and in absolute mint condition could fetch up to $62,000 AUD. If it has been circulated but still in good condition, it might fetch anything from $1,500 to $18,500 AUD. There were only 15,000 minted. An Australian 1923 bronze Halfpenny (George V)(Proof), uncirculated and in absolute mint condition could fetch up to $350,000 AUD. A reputable coin dealer will be able to give a more accurate valuation. After the 1930 Penny, the Australian 1923 Halfpenny is the second rarest of Australian Coins.
I have been unable to find a comprehensive listing of Australian predecimal coin mintage figures on the internet, but the average coin catalogue should contain the figures you are looking for. Your local library may have one of the following coin catalogues specialising in Australian coins - "Pocket Guide to Australian Coins and banknotes" by Greg McDonald. "Renniks Australian Coin & Banknote Values" edited by Ian or Alan Pitt. or "The Standard Catalog of World Coins".