Any coin with a "genuine" minting flaw would have some value, above the usual, as a collectible coin.
Genuinely flawed coins are not necessarily known about or documented until somebody turns up with one, since they are an "accident" of the minting process, and have escaped detection during quality control at the mint therefore, a valuation cannot be anticipated.
A reputable coin dealer should be able to identify and confirm the coin as genuine and make a valuation.
A sixpence was worth 1/40 of a pound so it would be worth about $.04. (1/40 of $1.61)
16.5 pence
Under pre-decimal currency in the UK, a shilling was worth twelve pence, and a sixpence worth six pence. The UK adopted decimal currency in 1971.
Good luck if you have one, but the last British Sixpence was minted in 1967.
$1.50
2.5 pence
Not enough information. Has it been circulated? Is there anything unique about it? Whose signature is on the front? Notes printed from 1966-1972 will have "COMMONWEALTH OF AUSTRALIA" printed at the top, front and back. Notes printed from 1974-1991 will have only "AUSTRALIA" printed at the top, front and back.
Two Shillings and Sixpence, or a Halfcrown, has been a part of the British currency for hundreds of years. I will assume that you mean a more recent year prior to the currency becoming redundant. Two Shillings and Sixpence GBP in 1966 had the purchasing power of about £1.56 GBP today. Two Shillings and Sixpence GBP in 1966 had the purchasing power of about €0.80 EUR today. NOTE - This historical conversion is the result of many calculations and considerations by a purpose designed program for which I can take no credit. The resulting answer should only be regarded as an approximation.
Modified coins have no collector value.
how much is a matt guokas 1966-76 card worth
its worth $5.00
However much the paper that it is printed on is worth....