Green’s Dictionary of Slang

half-a-dollar n.¹

a collar.

1893		P.H. Emerson Signor Lippo 55: One day he walked straight into this kitchen clobbered in a pair of rounds, tight to his legs, [...] and ’alf a dollar round his bushell and a long sleeve cadi on his napper.
1924		Mail (Adelaide) 16 Feb. 1/4: A few of the ways that clothes are referred to:— Collar— [...] Half a dollar.
1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.
1981		P. Wright Cockney Dialect and Sl. 106: ’alf a dollar ‘collar’.