with approx 3
This seems pretty straightforward. We’d need a Bluetooth-capable Arduino, an MP3 player hat, some buttons, a slider pot, power and (optionally) audio jacks, a box to put it all in, and a wall brick. I imagine the material cost would be around CDN$ 75. (maybe US$50?). There would also be a little bit of software to scan buttons and control the player hat, nothing too serious.
Frankly, I don’t envy anyone who’s challenged by a basic MP3 player having to deal with BlueTooth pairing, but maybe if she doesn’t ever try to connect with anything else, it will just keep working after pairing it the first time. 🙂
Contact me if you’d like to move ahead on this.