How cash works in Build and Kill Zombies
Cash is the whole progression. The game’s own promotional image is a before-and-after: a bare starter car labelled $0,1 next to a black, glowing, heavily armed one labelled $1,542,848. Nothing else gates the upgrade path.
There are exactly two sources
The 2x Cash pass has to declare what it doubles, and it does: “Works both cash earned by killing zombies and distance travelling”. That footnote is the only first-hand statement anywhere about how this game pays out, and it names two things and stops.
It fits the game’s own tagline, which asks how far your car survives rather than how long.
Cash while you are away
The game’s icon on Roblox carries a red banner reading “Drives offline”. That is the developer’s own advertising, on the first thing anyone sees, so the feature exists. How much it earns, whether it needs anything set up first, and whether it is capped are not described anywhere — not in the game description, not by any publisher.
What we will not tell you
The rate. No source gives cash per zombie or cash per metre, and the guides that offer “fastest farming” routines do not say where their numbers came from. Buying the 2x pass doubles an amount nobody has measured.