Here in the EU-zone, the M50's have never even been that cheap. Pretty much the same as DT770 80's. I've owned both (AT's are gone) and I guess people just got on with the M50-hype too much. Beyers have better comfort, build, bass and especially soundstage & treble. Highs on the AT's are basically quite sibilant and the overall sound sig is "shouty" with little air to speak of.
CAL1 is in SQ terms better than either, but they are a very different, a not-really-closed design vs good isolation and sturdy build on the others. If they ever achieve that CAL1 sound in a truly closed set, I'd happily pay many times their price for a pair. My Momentum or M100 are not as good sound-wise, but yeah, they isolate noise well when on the move.