Generally, the universally agreed entry level hi-fi headphone is the Grado SR60. It costs about $60, and though some people end up with other model the $60 Grado is something that you really should try. One of the reason is that Grado is a name that you will hear a lot in this hobby, and it’s a good idea to know what the “Grado” sound is all about. While most audiophile headphones require an amplifier, the SR60 doesn’t and can be plugged straight into an Ipod. late 2008, the SR60 has been improved and is now called the SR60i.
Other than the SR60, you have the AKG K66 which is actually fuller sounding and cheaper (selling for $40), but doesn’t have the reputation that the SR60 does. The K66 has siblings that are the K44, K55, K77, and K99. I believe the K44, 55, and 66 are now discontinued in a lot of countries. But retailers like amazon.com still carry them. I really have no reason to recommend the K44 and K55, seeing the K66 is selling at only ~$40. The K55 and K44, however, is a closed design, so outside noise are blocked slightly, but at the cost of inferior sound quality to the semi-open K66. The K55 eventually was replaced by the K77, and the K66 replaced by the K99. I really haven’t heard the K77 and the K99, and newer aren’t necessarily better sounding in this hobby, so I would recommend the K66 as an alternative to the SR60.
Another popular entry level is the Sennheiser PX100, selling for ~$40. Small in size and foldable, they offer good sound quality, though the SR60 arguably is the overall better headphone. The SR60 can be considered a full-size cans, though it falls on the small size of the full-size category. The PX100, however, is definitely a portable headphone. If you are interested in something small like the PX100, there are other models for about the same size and price, such as the AKG K412 from AKG and the Portapro from Koss.
The Portapro is a model that has been selling for 25 years, and it is actually the benchmark of portable headphones. People have a hard time believing that a driver that small can produce a sound that big! Koss recently released a 25th Anniversary Portapro, which sells for about $80. Though more expensive than the regular Portapro and the PX100 that it competes against, the 25th Anniversary Portapro is really one of the best portable headphone that you can buy.
Of course there are millions of other sub-$100 headphones, and Headfonia will do reviews on the great ones, but generally you can start with these guidelines. The options really open up once you go up the $100-$300 range. However, most headphone above the $100 mark will need an amplifier, so that’s really not considered entry level. Upwards of $300 you can start talking “top-of-the-line” with models such as the AKG K701 and Sennheiser HD650. The so called Top-Fi cans, however, comes in at $1000 and more.
Enjoy the journey!