If you have a good policy. The money doesn't run out. Because it isn't spending money but investing it.
Say this project cost $10,000,000 a year, and it allows say 10,000 families to use these services that allows them to get jobs, or make an additional $10,000 a year additional funding. Then their taxes would go back to pay for the project, these people otherwise wouldn't be making the additional money, their income tax wouldn't be paying for such a service, as well they will need additional services such as food stamps and Medicare.
Policy that help people gain wealth, in general pay for themselves, even if not everyone can benefit from it, but a small portion can actually pay for such services. Thus not run out of money.