I have spent some time looking at the low end car amps and the Blaupunkt AMP1604 stood out at $65 (here in the US anyway) https://www.amazon.com/Blaupunkt-4-Channel-Full-Range-Amplifier-AMP1604/dp/B07Q28CNSN/ref=sr_1_1
It has speaker level input and separate high pass and low pass options. As mentioned it will need it's own 12v power supply. I would guess for pinball volume, a fanless 10A unit should do the trick. The only downside is that is on the large side.