Studio headphone is one of the most important element for audio production because if you don’t have good quality studio reference headphones you cannot mix real well.
The reason you have to invest in a really good quality flat response headphone is because you have to listen to the sound as it is, in mixing flat response is must , flat response will help you analyze the low , mid and the high as it is and it will not add any kinda color or texture to the different set of frequency ranges.
See Hi Fi headphone are not atall same as a studio headset , the Hi Fi headphones may have sound enhancement modules, usually the bass boost which can make the song sound real balanced and nowadays in most of the expensive headsets you are going to get well balanced sound , so as a producer it is not a good deal for you.
All the headphones have a certain type of frequency response & dynamic range, so the flatter it is the better it is for you to mix , see along with a nice pair of flat response studio headphones you will also require one low end headphone , earpod and a high quality retail headphone, the reason you will need all this because you have to listen to the output across multiple audio devices , because each one has its own sonic character and will render a different audio experience , once you are aware of these characteristics then it will be easy for you to make the necessary changes.
In my opinion buy lot of cheap headsets and buy few mid and high range ear buds, it will give you a great idea about how your mix is going to sound across multiple hardware format , obviously monitors come into play aswell but in this abstract I will only talk about headphones , in order to make it easy for you I will drop down few super amazing studio headphones which I have hand on experience , they are super affordable and do have flat response , you can never find 100% flat response headphones, but you can find the best one which are kinda closer to the ideal flatter response, I mean a rig which can be transparent enough to get the right sound.
Down below i am sharing some real cool studio headsets that you can buy under the range of 200 USD, let me tell you these head phones are simply amazing and they have high level of transparency and have been widely leveraged across the audio engineer community.