One Sovereign GBP in 1909 had the purchasing power of about £69.42 GBP today.
NOTE - This historical conversion is the result of many calculations and considerations for which I cannot take credit. The resulting answer should only be regarded as an approximation.
$300Billion
Modern sovereigns unless in proof condition are generally only worth bullion. At the moment a full sovereign is worth about $400 US/CAD in gold.
Such a coin does not exist. The first Quarter-Sovereign coin ever produced by the Royal Mint was minted in 2009.
All Sovereign coinage issued by the Royal Mint since 1817 is 22 carat gold. These include the Five Pound (Quintuple Sovereign), Two Pound (Double Sovereign), Sovereign, Half-Sovereign and, in 2009, the Quarter-Sovereign.
Any collector value would depend on the year and condition of the coin. At the very least, it will be worth whatever the current price of gold might be. A mint condition Sovereign contains 7.322381 grams of gold. Currently gold is at about $1,790 USD per ounce. That makes the gold content of a Sovereign coin worth about $79 USD.
A British 2012 22 carat gold Quarter-Sovereign coin (Elizabeth II),(boxed Proof) is currently retailing for £130 GBP from the Royal Mint.
July 24, 2009 Gold plating a coin destroys its numismatic value. The Bicentennial quarter is worth but a quarter plus the value of the bit of gold used to plate it.
It's a novelty item worth couple of cents for the gold plating plus whatever the underlying quarter is worth. If the quarter is copper-nickel, then it's only worth a quarter. If it's a special silver "prestige" quarter made in San Francisco it's at least worth maybe $3.50 for its metal content.
200.00
500 USD
200000
The Royal Mint has never produced a Quarter-Sovereign coin until 2009. There has never been a need for a Quarter-Sovereign coin, since the Crown (Five Shillings) did the job and, after decimalisation, the 25 Pence coin to a lesser extent. The current interest shown in a Quarter-Sovereign coin seems to stem from a disreputable somebody claiming to have scooped the world market on a finite number of coins only available to them and, mysteriously originating in Another Country. These coins are not legal tender in Britain and, if they are actually made from gold, would be worth bullion value.