You can buy a portable unit for like 300e and seal the window with a piece of plexiglass with a hole in it. It's a pretty low barrier.

Sort of. We dont have sliding windows. Windows tilt in Germany so it's a weird shape you need to close up. Portable ACs come with a mesh cover that works OK but its not as good as a properly sealed window. They're also significantly less efficient and much louder.

Midea has released the Porta split a few hears ago which was a game changer for many people. I currently have one cooling the bedroom.