If your max budget for your in ear headphones is 100 dollars, then there is no doubt that you can find one within your price range since this is more or less a decent budget. But do note, if you’re a serious audiophile the ones listed here may fall below your expectations. The best in ear headphones under 100 are found below:

Bose delivers another superb product with a great price to boot. It delivers excellent sound quality both for voice and music. StayHear feature also raises comfort level and stability.
Monster Turbine High-Performance In-Ear Speakers is currently on sale!
Claiming to be as good as the expensive headphones without the hefty price tag is a great feat in itself. Luckily, the Monster turbine delivers with clear powerful sound that is built to last.
NuForce NE-700X Audiophile-Grade Earphones is priced at only $65
NuForce may not be a popular brand which may be the main reason why this doesn’t have the same number of reviews as the previous reviewed headphones. Nevertheless, it still has a bit over a hundred reviews which means it’s worth something. And indeed it is. These are one of the best headphones under $100.
Klipsch IMAGE S4 In-Ear Enhanced Bass Noise-Isolating Headphones – price not displayed by amazon because it’s below the SRP
Suggested by one of our readers, the Klipsch S54 has over a thousand reviews at amazon, which in itself is quite an accomplishment and says a lot about this product. Add to that Jay’s Siegel (from examiner) testimonial – “Hands down, these are the most comfortable in-ear headphones I’ve ever used!” and you certainly have gotten yourself a winner. Even though these headphones are from way back 2009, the quality is still great. But if you need more updated features (3 years is quite a long time too), we suggest to go with a more recent model the Klipsch IMAGE S4i which is still within your budget.