get by on
phr. v..phr. v.. to have just enough of something, like money or sleep, to survive or finish a task.
phr. v.. to manage or survive with a limited amount of a specific resource; typically used with money, sleep, or food.
I can get by on five hours of sleep.
When he was a student, he had to get by on a very small budget every month.
The small non-profit organization managed to get by on private donations and local grants for nearly a decade before securing government funding.
usually followed by a noun representing the resource being used.
contrast with 'get by' (used without an object to mean 'manage generally') to show how 'on' introduces the specific means of survival.
He gets by on with very little money.He gets by on very little money.the preposition 'on' already connects the verb to the resource; adding 'with' is redundant and incorrect.