Do these headphones need to isolate or contain their music? I ask because you mention "school."
That said, the HFI-2400 are very good, yes. Compared to the Grados they're a different beast - darker, bassier, more spacious sounding. But like the Grados - completely open. Makes them a no-no for use on trains, planes, and automobiles, as well as places like libraries (they leak too much noise in and out).
For what you're describing, the DJ100 are a good choice honestly (and they look pretty stylish IMO - black aluminum and silver accents - if it does anything for you, there's also a commemorative edition that celebrates Tony Bennett), so are the SR-80, and so are the HFI-2400 (although I like the HFI-2400 better for grunge (if there's a headphone that fits grunge as a genre, the HFI-2400 are as close as I've ever found)).
When it comes to the Beats, the only ones around $150 that I'm aware of the on-ear model, and they sound hideous (it sounds like you're listening through a woofer with no LPF); nothing I'd want to listen to guitars and wailing on. I have less of an opinion about SkullCandy - I (unfortunately) have experienced most of their original headphones, but that is apparently a bad reference compared to some of their newer models.
I'm guessing within your price range, some of the closed Ultrasone models would be suggestable, but I haven't heard any of the modern ones (like the HFI-780 for example); just based on the brand's reputation and what I have owned from them, I'd say give'em a look, look for reviews, that sort of thing. There's also the Ultrasone Fan Club thread that you could ask in - I'm sure someone there will be able to better guide you regarding the newer closed models.
As far as the lack of testing - I'd say go with Amazon.com if you can; their return policy is bulletproof, and you should have no issues sending back a pair of cans if you're unhappy.