What each price tier actually buys you

How much do I need to spend to emulate PS2, GameCube or Dreamcast?

Two findings do most of the work here. Under $80 already covers everything through PS1 plus Dreamcast. And the over $300 tier adds no system that a cheaper device does not already reach. Above a certain point you are paying for upscaling, screens and build quality, not for new libraries.

Ratings here mean a system runs. They say nothing about whether a device is pleasant to hold, how the screen looks, or how long the battery lasts, and those are usually what decides which handheld someone keeps using.