An Irish "Millennium" coin, with a face value of one Irish punt (or "pound"), is worth about US$7.50 in Uncirculated condition and about US$8.50 in Proof.
Ireland does not use the dollar and never has, so there is no such thing as an Irish 1 dollar coin. Ireland was using the pound in 1952, but there was no 1 pound coin. So whatever coin you have, cannot be either an Irish one dollar coin nor an Irish one pound coin from 1952.
$80 to $120
These coins were not minted by the Royal Mint and are possibly worth what you paid for them.
The Eire (Irish) Punt (Pound) coin was first issued in 1990.
That would be a coin of the Irish pound, which has since been replaced by the euro.
An Eire (Irish) 2000 cupro-nickel Punt (One Pound)(Millennium), uncirculated and in absolute mint condition could fetch up to £5 GBP. An Eire (Irish) 2000 silver Punt (One Pound)(Millennium)(Proof piedfort), uncirculated and in absolute mint condition could fetch up to £35 GBP. A reputable coin dealer will be able to give a more accurate valuation.
£5,000,000
It's worth exactly one pound.
A 1889 gold 5 pound coin is worth 5 pounds of gold, while a 1889 2 pound gold coin is only worth 2 pounds of gold.
Such a coin does not exist. The English have never produced a 4 Pound coin.
Nothing, the coin is part of an obsolete currency. Collector values - An Eire (Irish) 1988 cupro-nickel 50 Pence coin (Dublin Millennium), uncirculated and in absolute mint condition could fetch up to £5 GBP. If it has been circulated, not much. An Eire (Irish) 1988 cupro-nickel 50 Pence coin (Dublin Millennium)(Proof FDC), uncirculated and in absolute mint condition could fetch up to £25 GBP. A reputable coin dealer will be able to give a more accurate valuation.
£30.000