The used vehicle prices seem very high compared to past years,
but if the NOx pollution regulations are going to be tightened to such an extreme that gas/diesel engines will be BOTH expensive and get worse fuel economy,
perhaps the market is sending a “sober signal” and not a “foolish frenzy.”

Looking backwards, about the year 1997 government actions killed the reasons to own a diesel vehicle, but it took awhile for this to be apparent to vehicle users.

Why are USA used vehicle prices rising so fast?
Here is a foreign article that makes a strong argument that it is not just a shortage of chips for new vehicles,
but that prices in general are rising sharply (inflation) due to “the big picture” of world trade, especially USA and mainland China:

https://asiatimes.com/2021/07/will-china-bail-out-biden/

Warning: it is a long read.

sample quote

But Jin adds: “Now the United States has issued a massive amount of excess currency due to the epidemic, and the amount of currency issuance far exceeds the normal needs of economic development, so there is a situation in which more currency is issued but production cannot be restored. Inflation in the United States is rising, which will put a lot of pressure on the US finances. The US federal debt is approaching $30 trillion.

“What does this imply? At present, the interest on US Treasury bonds is more than 1% point, and the annual interest payment is about $300 billion US dollars, which is considered to be affordable. But if inflation approaches 5% or even exceeds 5% (interest rates will definitely follow after inflation exceeds 5), then the United States will need $1.5 trillion a year to repay the interest of 30 trillion federal treasury bonds, which will definitely lead to the bankruptcy of the government.”

Jin continued: “So the United States is actually looking to China now. You may have noticed that in the past, the United States has always said that China manipulated the RMB ( “Yuan” ) exchange rate and artificially lowered the RMB exchange rate. However, recently, the tone of the United States has completely changed… Why don’t you ask for appreciation? Because our things become more expensive as soon as the renminbi appreciates, and the United States must import our goods, and that adds to inflationary pressure.”

Treasury Secretary Janet Yellen said some weeks ago that tariffs on Chinese goods had hurt American consumers, Jin noted, adding that “it is very likely that Yellen will cancel the tariffs imposed on China within this year.”

end quote

This is nuts but for grins I was looking at used mustangs. Basically, I could sell my 06GT for $5500 more than I paid for it 6 years ago.

Wall Street Journal has an article on page A3 of Tues Aug 3 edition saying the Feds will issue new regs for vehicles of model year 2026.
Required MPG will go up:
average fleet mpg at 55 mph level driving must be above 54.5 MPG
and combined highway/city must be above 36 MPG

Tailpipe emissions will be “tightened” too
but the article does not mention what new NOx per mile level

The former 2016-2020 administration had “loosened” the MPG requirement to 40 MPG at steady 55 MPG and 29 MPG combined.

My estimation is that gasoline powered Toyota Prius type vehicles could meet these new regs.

Electric pickups and large electric SUVs might meet the new regs,
but only because of the “crazy” official math
where they convert range on a battery to an “equivalent” petroleum MPG.