I think you might have a slow leak around the caliper fitting.

You add some fluid to temporarily fixed the problem. But the fluid is still leaking, and it is dangerous because the speed of leaking might accelarate. Then you will find yourself having no brake when you need it most.

If you really want to save money, start learning how to fix little problems with your car. Otherwise, just try to shop around and find a shop that would fix it for less.