A good pair of canal-phones that fit properly should provide enough noise isolation (on the order of 25-40 dB, depending on design) that active cancellation is

A good pair of canal-phones that fit properly should provide enough noise isolation (on the order of 25-40 dB, depending on design) that active cancellation is unnecessary in most environments. People performing in front of heavy-duty speaker stacks often use canal-phones to be able to hear what they're doing without going deaf. The caveat is you really do need to mess around with different tips to find ones that fit and shove those suckers in deep enough to get a good seal, which a lot of people hate doing. Noise cancellation is great to have in over-ear cans but would be of very limited utility in canal-phones, assuming their isolation doesn't suck. $300 will get you a very good pair of Etymotics or Shures, which you should be able to get very good isolation with. If you can afford more, custom molded canal-phones are the gold standard. I've heard, in many places, that Bose's noise-cancelling over-ear cans are decent though.