If the "mint marks" on the reverse are the letters "F" and "G," then these aren't mint marks at all, but the initials of Frank Gasparo, the designer of the half dollar's reverse. In that case, you have an ordinary 1989-P half dollar, which will run between $1 and $90, depending on the coin's condition, as of May 27, 2007. If the "mint marks" on the reverse are something else, then your coin is best evaluated by a professional coin dealer who specializes in error coins.
Britain did not produce a "Dollar" coin.
The coin is still in circulation and is face value.
$200
The British do not have a Twenty Dollar coin.
An Australian 1989 One Dollar coin (Proof mint set only) could fetch up to $12 AUD. A reputable coin dealer will be able to give a more accurate valuation.
A "one dollar" coin has the value of one dollar!
As of today 1-28-10 value is $107.72 the coin is one tenth ounce of pure gold.
A particularly nice one might sell for a dollar.
value of 1845 us five dollar coin
1926 ten dollar gold coin value
the worth value of the liberty dollar coin is worth 50cents.
There is no such thing as a British 20 dollar coin. If you have a 20 dollar coin it must come from some other country (or even British colony)