https://www.minneapolisfed.org/institute/working-papers/17-13.pdf
... When immigrants are assigned the marginal cost of public goods, their fiscal impact is actually significantly less negative than that of natives. Immigrants’ tax contributions cover 93 percent of their publicly provided benefits while natives’ contributions cover only 77 percent of theirs. The dreary overall fiscal scenario is due to large public deficits and high national debt; problems that were much less pronounced in the 1997 report. In addition, natives have grown more costly over time because they have become an older population; their health costs impose a disproportionate burden on the federal government because it pays for Medicare and subsidizes related expenses such as nursing homes. Meanwhile, immigrants are more costly than natives at the state and local level because they have lower incomes and more minor children; this means immigrants are particularly burdensome to state and local governments which pay for public schools.
...
The above is from a 2017 Minneapolis Fed report. It gives numbers for immigrants without breaking out the numbers for illegal/undocumented immigrants.
The NY Post article says "the lifetime cost to taxpayers of each illegal immigrant is over $80,000." It says only that it got the number from a study "a few years back" without proper citation and without specifying which year. So, taking the numbers from 2018 (before COVID):
2018 US federal deficit was $779 Billion.
Divide that by 330 million Americans = $2,360.61 per capita.
Multiply that by 75 years of life = $177,045
That's a lifetime net fiscal impact of negative $177k per American! If we take the NY Post's quoted figure of negative $80k per illegal/undocumented immigrant, it would seem we are getting a bargain with the illegal/undocumented immigrants compared to the average American. Heck, the average American's net fiscal impact is more than twice as negative as the average illegal/undocumented immigrant's net fiscal impact.