It looks like f(x)’s Amber has Ultimate Ears 700 earphones by Logitech. These earphones, unlike her others, are relatively cheap in comparison. These run about 199$ at retail, but you can get them for 169.94$ on Amazon, or possibly less on other sites. These seem to be discontinued, as they are not found on the main earphone page on the ultimate ears website, but you can easily buy them online. In some cases, you might be able to find them in your local store, since these used to be in some stores like Bestbuy.