In general for $100.00 US you can get a quality set with one dynamic speaker, or a set of entry-level monitors with one balanced armature driver.
Your choices go up $200.00 two drivers, or $300.00 for three. The biggest jump in sound is from buds to, earphones in the $100.00 - $150.00 area. There is reported to be a noticeable jump when you go to two drivers. The move to three drivers is much subtler. That is unless you listen to the SM3 crowd with this months imported flavor of the month.
You have a lot of choices, look at IEM’s about 25% more than you can afford to spend right now. You could have these for a long time, so don’t rush into trading up. You can't start with price because, you can pay more, and you will find that the better stuff is available for less. Start with what you would want for earphones as if cost was no object, then compromise down to what you can afford next month. Life is too short to listen to cheap in-ear-headphones.
Edited by Sumflow - 6/18/10 at 4:12am