Thanks Scots (yes, that's why I went after it). But its from 1974 (2nd issue) & only dear because of its oddly popular denomination. Now for the 1971 $10 & $25 (which will be tougher/dearer than the latter74 issue). Could take some time to find those 2.
At last I can post the latest addition to my banknote collection in this thread - the new Bank of England £20!
The reverse of the note depicts painter JMW Turner and his masterpiece 'The Fighting Temeraire'. The Temeraire warship was launched in 1798 and saw action at Trafalgar. The painting shows her being towed by a tug up the Thames to be broken up for scrap in 1838.