Quantity   Component name
1 × TPA3116 amplifier board I used this one, but it is available in a bunch of places. $20 https://www.amazon.com/gp/product/B01MZ0IZMW/
1 × Power supply The board calls out 24VDC, though in later testing I found that 12V worked. The lower voltage may not put out the same power, especially with an 8ohm load. I used this one which was plenty. Note that if this really was putting out 100w*2, a 5A24V supply wouldn't be sufficient. In testing with two 4ohm loads, current was peaking around 4A, so it may not be possible to practially get ths 100w*2 output. $20 https://www.amazon.com/gp/product/B01GC6VS8I/ I intentionally used an external brick power supply instead of building it into the case with the amplifer to separate switching noise.
1 × Case I used the case from a Linksys wifi router I thrifted for $2
1 × Volume potentiometer and knob I pulled a stereo, audio-taper potentiometer and knob from my stock.
4 × Speaker wire terminals I used some simple banana jack sockets I had in stock. I decided to use these instead of full binding posts to keep the size down, and I knew I would want my speaker wires to already be terminated for easy setup on site.
4 × Speakers I eventually found 4 matched speakers, Sony SS-MSP75 at the thrift for $2/ea. They are small and sound good. Bass is what you might expect for such small speakers. Rated 100w each, no worries there. They are 8ohm, so the amplifier can drive 2 in parallel for each channel.
4 × Speaker wire I used old salvaged telecom wire(think Cat 5, but lower speed) from my stock. I also pulled out some dual banana plugs to more easily connect the wire to the amplifier.