Yeah, this is where the money part starts to get more interesting. Short partial shutdowns don't usually end up having any real dollar cost.
When you've gone this long, you start getting backlogs that have to be made up for. Also, I guarantee you the National Park Service will get at least a $25 million plus up in the 2020 budget to pay for damage, repairs, extra maintenance, etc. incurred from slobs in all the parks we've been reading about. As one example. I'm sure there are a bunch of agencies that will get extra budget dough (i.e., taxpayer dollars) to cover things, whether real or made up, from the extended shutdown.
One small interesting thing I noted, and I don't know if correlation = causation, is that I sent in my 4th quarter estimated taxes to the IRS over two weeks ago, and the check still hasn't cleared. That usually only takes a few days from when I drop it in the mail. What will be interesting is if they are in fact holding off on processing estimated taxes and then I find myself with a late penalty because the taxes were not processed before the tax deadline (15JAN).