I think an average of $68K is extremely believable. One hospital visit, overnight stay, easily could cost that amount alone. One childbirth will easily exceed that. Many illegals don't contribute to the tax base since they are paid under the table. A net $68K is more than believable to me.
I believe its probably a net cost; however, Im not going to take a report from an agency with a clear agenda, a group that has constantly misled, a group that made "adjustments", all of which went in their favor, at face value. Taking a look at that report, I noticed how they took early really high Obama EITC fraud rates and extrapolted that to the entire illegal population to come up with a cost. They could have used the somewhat lower fraud rates under Trump or could have realized, as you correctly did, a lot of business is done with cash under the table. These type of "adjustments" just makes me discard their analysis as biased even if it might be directionally correct.
You do bring up an interesting argument about under the table taxes. A few years, the libs derailed Wal Mart for screwing over the federal govt by paying low wages. The thought process was fed govt was paying food stamps for Wal Mart employees due to low Wal Mart wages. One thing the libs failed to mention was if Wal Mart paid more in wages, they'd have less income and pay less in income taxes. A 5,000 bump in wages would equal a $1,750 reduction in federal taxes at 35%.They conveniently ignored the revenue coming in from the lower wages. A Wal Mart employee is in 0% bracket usually while Wal Mart was in 35% then.
So, why did I bring that up here. The farms/construction companies/hotels, etc are all benefiting from super cheap labor. Labor that increases income and what they pay to the IRS. A day laborer, legal or illegal, isnt paying much of anything in income taxes, to the IRS in income taxes. Same with a hotel maid. They are in the 0% bracket even if legal. A highly profitable California business, depending, how they are set up is paying 30-50% in income taxes. So, the more they pay people under the table or the more they pay under market, the more for the IRS. But much like the libs with Wal Mart, this revenue is conveniently ignored by CIS....