I did a bunch of research on head-fi.org, looking for the best closed over-ear headphones for under $100.
These are the best three I could find:
BossHiFi B8
Takstar Pro 82
NVX XPT100/Brainwavz HM5
The BossHiFi B8 can be found cheapest on Aliexpress, for under $65.
I bought mine from the following link, but the sale is over.
So don't follow this link; do an Aliexpress search.
The best photos can be found on their Amazon listing:
https://www.amazon.com/dp/B01HZ7QDBK
The Takstar Pro 82 can be bought from the manufacturer on Aliexpress for $63.89, in silver or black:
It's available elsewhere on Aliexpress and on eBay a little cheaper, but it might be best to get it from the manufacturer so that you get the latest version.
The NVX XPT100 and Brainwavz HM5 are clones of each other.
The NVX XPT100 can be bought at Amazon for $79.99:
https://www.amazon.com/NVX-Over-Ear-Headphones-ComfortMax-XPT100/dp/B0093PVTPS
It's unavailable outside the U.S. and Canada.
The Brainwavz HM5 can be bought on Amazon for $109.50
https://www.amazon.com/Brainwavz-HM5-Studio-Monitor-Headphones/dp/B006MA9XXM
It should be available in more countries, though I'm not sure which ones.
All of these headphones are supposed to sound amazing and be comfortable.
I chose the BossHiFi B8 because it's simple to change the earpads, while it is not so simple with the other headphones listed above.
The BossHiFi B8 is not good for people with small noggins; it's made for people with large or perhaps medium sized noggins.
Reviews of the BossHiFi B8 can be found here:
https://www.head-fi.org/showcase/bosshifi-b8.22425/reviews
Reviews of the Takstar Pro 82 can be found here:
https://www.head-fi.org/showcase/takstar-pro-82.22388/reviews
Here's a massive thread about the Takstar Pro 82:
https://www.head-fi.org/threads/takstar-pro-82-review-impressions-and-discussion-thread.849965/
Reviews of the NVX XPT100 can be found here:
Once I receive my new headphones, I'll report on how good they are.
In the meantime, if you have experience with these headphones, I'd like to hear it.
Or perhaps you think another pair of headphones are one of the best closed over-ear headphones for under $100?