I think that it's possible to think in those terms, but I think the cost of doing nothing would just mean that the government would have ended up being forced to do something anyway, but probably something even more expensive or even more radical than what the government felt that it had to do.
For example, in the absence of any income support measures or loans, as I mentioned, there would be widespread economic distress, bankruptcies and so on. You can easily imagine financial institutions in this country going under one after the other in such a catastrophic scenario. The government would have had to bail out banks, which probably would not be much cheaper, certainly not cheaper than what we are currently doing as a country to support individuals and businesses.
As for the cost of doing nothing, I don't think you can really envisage that because the government would have been forced to do something anyway. Instead of doing it in March, it would have had to do it in late April or May, probably at a much higher price than the total. That we will never know for sure because we don't want to run such a bad social experiment.