Decent mechanical toys for young teens, preferably under $100?

I've got a 14 year old nephew who basically lives on his phone when he visits, like pretty much all 14 year olds. Mostly it's games in his case. I've resigned myself to this, especially since I'm not his parent, but his birthday just came up and I want to get him a present that's not purely electronic, but more mechanical with perhaps some electronic aspects or features. He's into or was into LEGO, RC cars and drones, robots, etc. Again, like most boys his age.

I was actually wondering if there are any decent toys that incorporate gears and motors, under $100, that are worth getting. I've been teaching myself to fix cars, and have been studying how transmissions and differentials work, and it's quite complicated and fascinating, and I think that a kit that would model such devices might make a great toy for a young kid. Is there such a thing?

I don't mean the K'Nex, Hex or Lego-type toys that include motors and gears that you can use to build crude robots, vehicles or cranes. Those are great and he has a few of those, but I was thinking an actual scaled-down model of a transmission, differential or similarly complex real-world mechanical device, e.g. turbine, clock, etc. It would have both mechanical and electronic components, and be fairly well-built.

I think that kids spend too much time these days with virtual devices like phones and tablets and too little time with "real" things that they physically interact with. Ideally they'd be doing both, and learning how to combine the two using STEM devices like Arduino and Raspberry Pi.

Anyway, just wondering if anyone has any ideas or suggestions along these lines. I bet that such toys exist, but they're probably a lot more expensive than $100.