I find Grados to be horrible, loathsome things with a gargantuan mid-treble bump. Ick. They're poorly made, too.
For $100, I'd strongly consider a used pair of Beyerdynamic DT250s. They're pretty good. I've never heard the DT770s, but they're supposed to be even better. The DT880s are nearly unbeatable, but then again, the DT880s are way outside your price ranged - $170 is cheap for a used pair.
Also worth consideration is AKG's K240 and K270. You can get some used K240s on eBay for $70 or less, and they're immensely durable - even better than the Beyerdynamics, in this respect.
Come to think of it, I've got some open-modified DT770s I need to sell...