Quads are out there for $500-$600 easily. They're basically everything a MK series is but without the power amp. I absolutely love mine. The V-Twin is okay but it won't give you any of the qualities you'll get from the Quad. My favorite feature of the Quad is the ability to combine the channels. You can have 1, 2, 3, or all 4 channels on at once.
I've commented before that it provides much more of the Boogie MK tone than a Triaxis. Every component is full sized, and it will deliver more of the Boogie tone when used alone, without the Boogie
power amps. The Triamp (to me) needs to have the Boogie power (or something like it) to get you the Boogie tone. The Quad is more complete sounding, even when run direct, or through SS power, or a Peavey/Carvin/etc
tube power amp.