Green’s Dictionary of Slang

a price, a payment.

1861		Punch 27 Apr. 169: About $50. Now this is what the inferior members of the equestrian order call a high pike, and the vulgar in general denominate a heavy fork-out.
1910		Sun. Times (Perth) 17 Apr. 2nd sect. 9/1: They Say [...] That so cocksure was he that he had himself measured for three suits. That the fork-out will necessitate strict economy for many months.