Green’s Dictionary of Slang

line n.2

[? bottom line n.; Mezzrow & Wolfe Really the Blues (1946) ‘Line two means the price is a dollar; prices, like times of the day, are often doubled so that outsiders won’t understand the details’]
(US black)

1. money.

[US]A.J. Pollock Und. Speaks.
H.B. Darrach Jr. ‘Sticktown Nocturne’ in Baltimore Sun (MD) 12 Aug. A-1/1: A barnacle is a derelict of the old fleet; it is a point of honor among seamen who have any ‘line’ never to refuse a barnacle a belt.
[US]A.S. Fleischman Venetian Blonde (2006) 141: Now I was short of lines [...] he’d help me.
[US]‘Iceberg Slim’ Pimp 188: What kinda lines you got?
[UK](con. 1930s–50s) D. Wells Night People 118: Line. Money. When borrowing, ‘line’ doubles the amount actually required. Thus, ‘line fifty soft’ indicates a need for twenty-five cents and ‘line fifty hard’ for twenty-five dollars.

2. the cost or price of an item.

[US]Cab Calloway New Hepsters Dict. in Calloway (1976) 257: line (n.): cost, price, money. Ex., ‘What is the line on this drape’ (how much does this suit cost)? ‘Have you got the line in the mouse’ (do you have the cash in your pocket)? (Also, in replying, all figures are doubled. Ex., ‘This drape is line forty’ (this suit costs twenty dollars).
[US]Mezzrow & Wolfe Really the Blues 218: Hold it down, Jim, and I’ll come up with line two like I said.