Now if we're talking 4-channel budget amp, once again I would have to go with a Kenwood, specifically the KAC-M3004.
BigDWiz did an amp dyno on this particular model, and despite being the size of a cellphone, it performed well beyond its rated power.
I had one and loved it, only replaced because I love the JBL MS-a1004 more. I sold my KAC-M3004 for $70, which is a pretty typical price for one in used condition. While a new M3004 will run you about $100.
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