You are in luck because tow of the industry standard headphones used in the recording industry cost about $100.
Headphones used by engineers and artists are different then the used by home HiFi enthusiast in that the studio headphones are generally more accurate and "flat"
But there are two basic kinds.
(1) those used use by the engineers, these don't need to keep outside sounds away because there are used in a quiet environment. and they don't need to contain the sound and can "leak" sound out into the room. My AKG K240 headphones are what is called "semi-open" and leak sound in both directions but are VERY flat and very accurate and cost only $99
(2) those used by recording artists. The above K240 are not used anyplace near an open microphone as sound will leak into the mic. this person need bater isolation for a guide track does not get picked up by the mic. But on the other hand these don't have to be great headphones because all the artist needs to get is the pitch and time. They are NOT listening for details as some times all there is in the headphones is a metronome track or just a piano track. You don't need to spend a lot
(3) home stereo listening is not the same as recording.
Look at these, they are VERY common in professional work
http://www.sweetwater.com/store/detail/MDR7506
http://www.sweetwater.com/store/detail/K240S
For a given price you get better sound with "open" headsets because they are technically easier to build but yu have the problem of no sound isolation. THat's not a problem in some use cases, like recording studios but is a big problem in places like the metro train or an airplane.
I have a number of headphones and anytime use a really cheap pair for practicing guitar or keyboard, some times even $25 earbuds for that. Much of the time you don't need great headphones
Mixing for video is again different than practicing guitar so you have to say what is is exactly you are trying to do. But in any case no need to spend more then about $100.
