My understanding is that a budget is simply an estimate of how much a project is likely to cost.
The way governments work is that they spend money that doesn't actually exist. Something like buying stuff with a credit card. The tax payer eventually has to pick up the bill and repay that debt.
The purpose of budgeting is simply to ensure that the level of debt never gets too much out of control.
So when a government says that a project will cost x amount of dollars it doesn't mean that it has allocated a certain amount of money and if there is any left over you can do something else with it. It simply means the a project is affordable and gives an estimate of how much it is likely to cost.
The way governments work is that they spend money that doesn't actually exist. Something like buying stuff with a credit card. The tax payer eventually has to pick up the bill and repay that debt.
The purpose of budgeting is simply to ensure that the level of debt never gets too much out of control.
So when a government says that a project will cost x amount of dollars it doesn't mean that it has allocated a certain amount of money and if there is any left over you can do something else with it. It simply means the a project is affordable and gives an estimate of how much it is likely to cost.