Other poster summed it up nicely, as there's a range of remedies from fees to lowering the payment you get to investigation to prison, but by far the most significant impact is this key metric:

Past Performance.

You can probably get away with screwing over the government once, maybe even twice. But good luck once you're legally and nationally blacklisted.

You might get paid extra to complete. Or you might get investigated by the Feds and The Congress.

https://en.m.wikipedia.org/wiki/Hughes_H-4_Hercules

It seems like I'm constantly hearing about large companies bidding at price x and then winning the bid, only to have the budget run over 10 times the original bid. So it seems in some cases the issue is becoming filthy rich as you rake in billions in profit from deliberately going over time and over budget.

Somewhere between late fees to congressional hearings depending on how badly things go.