TDK TW550 Bluetooth Speaker Set. The electronics work fine: Bluetooth continues to work perfectly, as does headphones output. However, one if not both of the speakers are blown. At low volumes you don't really notice it, but it becomes apparent the louder you turn it up.
Price: free! Maybe you like doing home repair projects--you could buy some new speakers and replace them yourself--or maybe you don't mind listening to music etc. at low volumes.
Power supply NOT included (you'll need to get your own 5V/2A adapter; btw, I've never used it with batteries, but presumably it works on batteries, too). The original power supply broke a decade ago, but I replaced it with the one linked-to below. I plan to keep that replacement so I can use it myself with other things if necessary, but for ¥500 I will include it with the speaker.