The M50 used to be able to be had around $100 new. It's not been that inexpensive lately. It has no sound stage, it's cramped, not that comfortable (to me at least) and the sound is pretty boring (some slightly bright highs, recessed mids, and bass is decent though). The only truly good thing in my mind about the M50 is that it is built well and is made like a tank and I like that it has 180 degree swivel cups. Other than that, I don't think it has $100~$150 sound.
Based on your genres, the HFI 580 would do you justice. I find the HFI 580 to have more sound stage, and more interesting/energetic sound than the M50. The ultrasone has that fun sound. Some people love it. Not everyone does. Only you can decide that. Anyhow, it's also less expensive retail wise, so another nice perk. Plenty of bass, nice mids, energetic highs. Looks nice too.
The 780 is not as harsh, dunno where they got that idea. The HFI 780 is a more smooth refined sound, less strong bass, same mids, slightly less treble. It's an excellent headphone, not `better' than the 580, simply a different sound, again, as they take the bass & treble down a notch for a smoother less bassy experience of the same sound. Great headpone so long as bass isn't the most important thing to you.
Check out the Shure DJ750. It's inexpensive, looks nice, swivels and folds, and is a bassy little monster. Doesn't get a lot of chatter around here like the Ultrasones do, but figure I'd throw it into the mix.
Another headphone for you to check out is the Denon D2000. If you can afford it, I would put you on it right away. It's in my opinion a nearly perfect mid-tier headphone and is very well suited to bassy electronic music, but can also turn around and handle acoustic and classical with authority too. Very easy to drive, no amp required, and it's classy looking (even the cable is sheathed). It's gorgeous. It's an excellent portable, and full size home headphone. It simple doesn't fold up or swivel, if that's a deal breaker. That said, if you need something less, check out the Denon D1100. I'd pretty comparable to the HFI 580, but maybe you would like the style better.
Another headphone that may interest you, although not considered a massive bassy headphone, is the Fischer Audio FA-003, which comes with both velour and leather pads, and is pretty nice looking to, and has excellent neutral audio.
And another headphone which may be of interest, is the KRK KNS8400. It has great sound and can do bass with some authority as well and isn't that expensive if you want a headphone with some good clarity.
Edited by MalVeauX - 9/8/11 at 5:46am