$1016, if I counted properly.
https://www.youtube.com/watch?v=wisuyHdsv-A
In the comments is mentioned a 12V high pressure motor/pump ( Pumptec Pumptec 107SS-105/M925 12V Pump & Motor ) as an alternative, but it's a $850 alone... and in the video, even using the 1500W inverter, he's making a gallon in under ~6 minutes of runtime. He estimates 100 watts per half gallon.
Not really saltwater-rated products, BUT - it's easy to make freshwater to clean them with, to make them last longer. Might need to replace the $79-99 pressure washer every few years, everything else looks like it would be OK WRT salt.
And looking at those, there are battery operated washers with enough PSI which may well work.