Those are less expensive and less dramatic than a typical NFL game. Rather understated, given our national culture.

The real issue is how much of the cost is unwritten by private entities and what they might expect in return.

That's really unconcerning compared to the bulk of political spending. Also, the money spent on inaugurations is easily trackable; it comes out of a general fund. Absolutely pales in comparison to Congressional insider trading and stuff like Hunter Biden and Eric Trump do: making money off of implied considerations.

Can you enumerate the costs of those inaugurations?

Well, Trump said there were a million people at his inauguration (I know, this was an absurd bald face lie). I don’t know how much it costs to rent, set up and take down that many chairs, but I’m going to guess it was more than three fifty.

At risk of picking nits: they don't put up a million chairs. I attended the 2012 inauguration and we all stood on the grass in the National Mall.

(I agree with your overall point though. There were speaker towers arranged at intervals down the mall and plenty of crowd control involved in getting people to and from the event in the first place, none of which had to have been cheap.)