The best option for the $100 range, and in fact you can find it for $50-$60 refurbished, is the Sony MDR-V6. Not the MDR-V600(inferior unit w/similar sounding model number). The MDR-V6 is identical to the MDR-7506 except for the name plate which has the model number on it and the plug(7506 has gold plated plug).
The MDR-V6 is built with far superior construction quality than any other headphone in the 100 dollar range, and in fact, is built better than most in the $500 range: it was designed for harsh studio use conditions/abuse. It has a stainless steel headband and stainless steel pivot frames/pins at the most stressed points of band pivoting/motion and has metal alloy outer can covers; the cable is of very strong construction and has a very high quality plug designed to last for many years without failure. The cable is firmly connected to a strain relief molded insert into the can cup junction. The headband is covered with a soft padding and synthetic leather piece that is double stitched into place. The ear pads last 2-5 years, depending on use conditions, and are readily replaceable for $20 from several sources.
It has a very flat response, with some minor issues(mainly a dip around 205Hz), but more accurate than anything else I know of in the price range, and in fact, more accurate than most things that cost much more. Now, many might not like this brutal accuracy, after they realize how poor many recordings are, or they might not like the minor imperfections in response that deviate from neutral, such as the 205Hz dip which causes a slight 'hollow/tin' sound to occur in the mid-range, if compared to a reference without the dip in that spectrum.
I have compared the headphone with live sources, using dead accurate measurement mics, with me standing between the mics and listening to the live source and headphones, and the sound is nearly identical in tonality and detail/resolution. It is a very high quality monitor/tracking headphone.
I can PM you where to get these refurbed for about $55 with shipping(and under $50 shipped if you buy like 4 at a time). I don't like to post where on public boards because the website does not advertise this product in the price finding search engines, and I have been buying this model phone for a couple of years from them to give to friends/family, etc and would like my source not to run out of prouct.

-Chris