A high pass filter is essentially a RC filter in which the resistor part can be the speaker coil, so one only needs two capacitors, one per channel, which would

A high pass filter is essentially a RC filter in which the resistor part can be the speaker coil, so one only needs two capacitors, one per channel, which would cost a lot less than $0.50 in small quantities (example: Vishay ZSC00BM2211AARL, 220 uF - 10Vdc: €0.14100 in 10 quantity at tme.eu, a lot less in 100 or 500 qty). The problem however is either the amplifier ic which is too powerful, or the speaker itself being too weak to sustain its power. That would be bad design though; one should never assume the signal won't contain certain frequencies; it's good practice to pick a speaker that can sustain at least twice the maximum amplifier power indefinitely, and even more during peaks, regardless of what frequencies are reproduced.