The ultimate w126 AC solution.
 

Reasonable.

The cost of that A/C unit and generator far exceeded the cost of rebuilding every single part of the stock A/C system in that car......and doesn't work as well as the stock system either. Stock system is good for 24000 BTU, I doubt seriously that window unit is anywhere even close.

He could save a couple hundred pounds if he got a really long extension cord.

Actually I ran the numbers and replacing everything (doing it yourself)- condens, evap, comp, dryer, aux fan, exp valve, hoses, seals, flush, oil, vacuum (vac pump cost), recharge (gauges cost) plus 24 hours labor would cost you more versus a window ac, generator and 1/2 hour labor.

Also doubt very much "stock sys is good for 24000btu"

Or drive along overhead electrified train tracks and run a pole up to the cables - might need a step-down transformer though which again adds weight.