Green’s Dictionary of Slang

three shillings.

1859		Hotten Dict. of Modern Sl. etc. 126: EARTH GENS [...] ERTH GENS, three shillings.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1873		Sl. Dict.
1892		Lloyd's Wkly Newspaper 3 Jan. 6/5: Here's erth-yeneps [...] and I wish it were erth-gens.