Look for a Class A/AB amp. There are quite a few which are very powerful. They run the first 10 or 20 watts in Class A then switch over to Class AB. Off the top of my head are Pass Labs, Plinius, and I think Parasound.
Ok stuff like your describing such as the x350.8 (among other similars) are indeed what he wants but way over budget
The OP also has to keep in mind that the heavy amps also tend to be better. There is a reason they are so heavy
Call me ignorant but if an amp is 25lbs or something like that i would automatically dismiss it. isolation is both heavy and expensive. Quality power supply is both heavy and expensive. Large custom toroidal transformers are heavy, and expensive. I can go on and on
I think your best bet is to keep it closer to 200watt @ 8 ohm and look in the $5-6k new department and hope to get 40-50% off in the used market