A Purifi based amp might be what you’re looking for. I have a March Audio amp (P502, discontinued) and am a fan of their build quality and incredible sonics, but they’re based in Australia. If small size is what you’re looking for, then you don’t really need monoblocks, and the P422 might fit the bill.
Even cheaper would be a Hypex based amp, and for that I would go to Audiophonics in France. Look for the NC502MP module, it’s 500 watts into 4 ohms, plenty of power and for many is indistinguishable from a Purifi. My amp is based on that module and it’s mighty fine and powerful, incredible detail and clarity with great bass drive and definition. I love it and don’t feel a need to upgrade to a Purifi at the moment.