Israel desalination plant profitably offering a fixed price of 1.45 NIS per cubic meter. At current exchange rates that is around 0.40$ per cubic meter (1000L).

https://www.gov.il/en/departments/news/desalination_260520

Freshwater withdrawals in the US (which includes all agricultural use including exported crops and animal feed) is around 1550 cubic meters per year.

https://ourworldindata.org/grapher/water-withdrawals-per-cap...

So, even if we replaced all freshwater use in the US with desalinated water at current prices it would only incur a additional cost of ~600$ per capita per year. If our water use were more similar to peer countrys such as Germany (410 m^3), France (475 m^3), Australia (724 m^3), or Japan (640 m^3) the per capita costs would only be ~150$-250$ per year.