I would look at in-ear monitors for your purposes. If the instrument levels are that high, they will bleed through even closed headphones. Shure, Etymotics, Westone, Ultimate Ears, and a few other companies make these. In your price range, I have used the Westone UM1 earphones and I like them a lot. Great midrange, highly accurate, fantastic isolation, and comfortable, but only go down to around 40 hz.