Automotive, in-tank fuel pumps are designed to be excellent gasoline “pushers” but since they are located in the tank, they don’t need to be strong “pullers”. When the pumps get weak, they start showing it at their weakest point. The pump gets weaker at lifting the fuel from the tank. The fuller the tank, the more easily it can pump fuel from the tank because the weight of the fuel is helping the pump.
By consistently running on “fumes” you are shortening the lifespan of your fuel pump. They require fuel to both lubricate and cool the pump. Starving them is not good. Therefore, it is a false economy to run very low on fuel as you risk damaging a very expensive to replace component.
It’s always a good idea to test things before replacing them to insure it is a likely culprit. When short on cash, it’s imperative. If it were mine, I would do a fuel pump pressure and volume test with the tank level below 1/8 full. If the pump is weak, it will likely show up in this test.
If it hasn’t been done recently, you might want to start with replacing the fuel filter. It’s cheap and easy to do and could be the cause of, or a contributor to the problem.
Before I actually replaced a pump that tested bad, I would make sure that the electrical supply to the pump was not compromised by corroded connections or a failing fuel pump relay that isn’t delivering the rated voltage and current.