It's worth noting that the Department of Transportation final ruling devotes a section to economic impact [1], and estimates a ~$55M increase in fees paid by passengers traveling with ESAs to airlines.

> The current policy amounts to a price restriction which requires that airlines forgo a potential revenue source, as airlines are currently prohibited from charging a pet fee for transporting emotional support animals

> Removing the current requirement that carriers must transport emotional support animals free of charge will allow market forces (i.e., carriers as producers and passengers as consumers) to set the price for air transportation of emotional support animals as pets. This provision will allow carriers to charge passengers traveling with emotional support animals (dogs and other accepted species on board of an aircraft) with pet transportation fees. This represents a transfer of surplus from passengers to airlines, and does not have implications for the net benefits calculation of the final rule."

[1] https://www.transportation.gov/sites/dot.gov/files/2020-12/S...