The reason it is so cheap is it is direct from china.
It is possible it is legitimate, as an Iphone for example only costs on the order of $20-50 to manufacture. This is pretty common. So if it is the real headphones, it is likely the seller is illegitimately selling the item direct from the chinease manufacturer. Without paying the normal royalties to the designer. This is a relatively common occurrence.
Other possibility is it is a fully legitimate product, it is just the price before shipping is added and the overhead for the American retailer.
At any rate, I would expect it to arrive anywhere from 2 weeks to 2 months from now. It is usually much cheaper to buy things direct from china, however the downside is usually the length of time the shipping takes and the expense. Also be aware there might be some customs charges involved, I'm not sure on that but something to think about.
The last possibility, is it is just a cheap imitation in fancy packaging. I would generally however expect to see a more known company being imitated. Though it greatly worries me that they put the word "authentic" in the title.
Lastly for the warranty, the costs involved with shipping the item to china, and then shipping it back to you will be more than the item is worth. Its possible the company might be nice and just send you a second pair without you needing to send the first one back. But I wouldn't count on it.
Approach warranties from Chinese companies as something that is in the realm of possibility, but not a given. (expect stall tactics, redirects, etc.)
The reason you buy from an American retailer is it is fast, and warranty claims are much easier, or it is much easier to deal with the company if it is being vagrant. But it will be expensive.
The reason you buy from a Chinese supplier is it will be cheap. But it will take a long time to get to you, and warranties are very difficult/expensive to get them to honor.
With things like this, if it feels too good to be true, it probably is; or it's not nearly as good of a deal as it appears.
To me personally the headphones wouldn't be worth the possible headache that would be involved.