The TDA7297 is a 2.0 Audio Amplifier Board, that can drive your old 4-8 ohm 10-50 watt speakers. I had a couple of old Bose cubes, and Cambridge Soundworks speakers lying around so this was a cheap way to give them a second wind.
They can be bought from eBay, Aliexpress or Taobao. Taobao’s the cheapest, but you would need to factor in shipping costs and it’s probably only worth it if you are getting other parts as well at the same time (which you should).
The sound quality is rather good too, although there’s a bit of buzz when there’s an open circuit – input audio jack not connected. Once everything is plugged in, the sound is clean and provides decent volume amplification.
The voltage regulator on it is quite flexible. It specifies a 12V input, but seems to work with anything from a USB DC 5V to 15V. It uses a standard DC jack adapter, or you can wire it up directly.
I am really quite happy with the sound quality from this $2 amplifier. It works well in tandem to my microphone pre-amplifier board which I also bought from Taobao for $4. You can find examples of sound quality on Youtube, e.g. https://www.youtube.com/watch?v=_fon0Mz-7ZU.
There’s a whole bunch of cheap electronics you can get from eBay. For example, if you want a little more functionality to the sound amplifier, you can get a board with Bluetooth audio profile (TDA7492). Could be something to consider for your next weekend project.