stereo integrity HT 18 $239 shipped from factory brand new
Also, most amplifiers for Professional Audio are Class-D and full range (up to 20khz). Until recently Class-D amps were mostly for subwoofer use in car audio. Building full range Class-D amps is harder and more expensive. The switching frequency must be high enough that harmonics will not affect audio quality at higher frequencies. This requires a switching speed of 100+khz which was hard to do until recently. You are right that mosfet amps have been around for a long time, but regular mosfet amps are Class A/B which is only ~45% efficient at converting power input to audio output.