I too am in a threadbare state, but it doesn't stop me spending money on (model) railways. I just spread the cost over several years, like what the Government would do.
Unlike me, the Government has the advantage of the multiplier effect - the fact that money spent goes round and round and round as firms and people spend the income they earn from major projects and pay taxes which then help to pay for another bit of the same project,,,,, and so on.
The Government can also print money. I would like to try that too, but doubt if I would have the same success.