This is one of the things (along with repair) that finally motivated me to learn electronics. You could probably build your own Everdrive 64 for less than $20! (Plus hundreds of dollars for an oscilloscope and other equipment but you can keep that for the next project)

Maybe worth it?

There are knockoffs for a lot less, the author here is even using one. But then you aren't supporting the inventor of the thing, just a factory that's churning them out somewhere.

Nobody asked, but I'll list differences I've noticed between the real everdrive and the knockoffs: Games that require a cartridge battery won't won't work correctly on the clones, the SD card slot is a lot cheaper on the clones, and the clone doesn't have a USB port (which I think is used for live game dev debugging?)

I assume there's a fair amount of work needed to develop these carts, but they probably don't ever sell in large quantities. Yes, it's expensive, but I can't imagine anyone getting rich out of manufacturing these. They are however instrumental for the hardware and software preservation purposes, so it's important for the community to support them.

It's interesting to note that the Everdrives are still actively manufactured in Ukraine, despite the immense difficulties caused by the war.