There was a big push towards developing chlorine-resistant chemistries a few years ago, but as far as I can tell, that has fallen into a “researchers don’t know what they’re doing, the plants are already designed around this problem” narrative. Of course, those plants are huge investments, and maybe it’s correct that one wouldn’t be able to take advantage of chlorine-resistant membranes until a new plant was built.
Cellulose triacetate RO membranes have chlorine tolerance, but have inferior chemical stability, productivity and selectivity to polyamide membranes, so it is sometimes used where chlorine tolerance is an issue. CTA membranes are also available in hollow fiber format, while polyamide membranes are essentially exclusively found in spiral wound configuration (some operators want fibers for higher fouling/solids feed). CTA is limited to a much smaller pH window (like 4-6 versus 2-12), and are not suitable for more aggressive cleaning methods, so I’m not sure if it overall provides a benefit versus polyamide RO with more aggressive cleaning cycles.
Free chlorine (technically assorted chlorine oxides like hypochlorite) attacks RO membranes, so now you have to deactivate your reactive species first. Usually UV lamps, you use sun, but now you need UV-clear tubing, not easy.
Reverse flow flushing can be done with the components you mention, that's another $20/50 plus sourcing logistics.
Yes, the theoretical expense in quality pumps is quality. There are tighter tolerances, beefier components, better polymers, and more QA. It all adds up.
It's still all fairly cheap by Western standards, but it's a tall ask for a lot of places that barely have potable water.
That combined with reverse flow flushing will probably last many years. And it can all be controlled by a 10 cent microcontroller, one pump, one valve, and a pressure sensor.
I don't doubt that high pressure pumps are bad... but that's just a design issue - there is nothing theoretically expensive about them.