subsist on (something)
1. To manage to survive on something as the sole or primary source of food. The unique creature has evolved to subsist on tiny organism carried by the stream into its ever-open mouth. When I was in college, I was so broke that I subsisted on nothing but rice, beans, and ramen noodles.
2. To eke out a living on something or some amount of money. I just can't subsist on the amount of money you're paying me, so I'll have to start looking for other work. I think you should go back to work, John, because the family can't subsist on my job alone anymore.
subsist on something
to exist on something; to stay alive on something. We can barely subsist on this amount of money. We need more! They are able to do no more than subsist on what Mrs. Harris is paid.
To survive by using something as a source of food: The people of the war-torn region subsisted on bread, water, and cheese for several months.