I installed a new Mitsubishi mini-split last year (third one in 25 years!), which struggles in really hot weather (also, not helped by it being a passive solar home).
They are screechingly expensive here (professional install, not DIY) but it does do a decent job except in extreme (over 100F) weather, which is rare here.
(It can also heat, but I have a boiler that is actually more efficient than a 1 year old Mitsu, so I only use it for heat occasionally as fall begins.)
While researching those, I found small (tiny, really) window units (small enough to fit in my casement style (hinged) windows) which are otherwise not generally adaptable to window AC units.
These small units regularly sell for around $100-150, usually on sale in summer, and, while
extremely noisy (and clearly not efficient at all), they do an ok job at cooling a small room. That helps reduce the load on the mini-split in an open plan house.
Just checked - I see small Hisense ones on sale now for around $100, rated at 5000 BTU, and are small enough to fit in an opened casement window (usually around 20 inches wide or so). Fitment I haven't yet worked out, but how hard can it be?

Reviews on the Hisense unit tend to be oddly positive - must be the low price? - with few complaints about noise or room cooling capability.
At that price, they are nearly disposable, and are light enough to be easy to install and remove, while 'normal' units (u-shaped or not, for double hung windows) tend to be really heavy, not a one person install, and not easy to remove when no longer needed.