There isn't really a "budget" stat separate from government spending; there is no surplus or deficits - the game treats you more or less as being precisely balanced. There may be issues about various departments being underfunded, but to my knowledge no issue yet exists about the broader government itself running a surplus or deficit. You can essentially treat the
government expenditure stat as your national budget. As for what makes up the government spending stat itself; it's pieced together from the various sub-stats like
defense or
business subsidization. Your total GDP is pieced together from all government spending areas combined with the value of all national industries (like
tourism or
mining). Your final
GDP is then the combined government + industries multiplied by your population (the precise formula of which I do not know). I hope that helps!