On-ears, eh? I'm bit of a fan of on-ear design. Over the years I've had a few.
- Fischer Audio Fa-004, Brainwavz HM5. These go by load of other names. You can get them quite cheap. These are not that fancy but they sound quite good. Comfort is quite decent (no swivel) so I think it's out then. Still, worthy consideration. They used to sell for $100 and people considered it a bargain. You can get maxell and other rebrands for like $10. Crazy value.
Kef M500
This here is my personal favorite. It cost like $300 new but these days you can score a new for less than $100 if you're lucky. Look into used ones. It's a damn fine headphone. For on ear it is spacious sounding, well balanced...and well. What can I tell you. I've had headphones that cost $2000 but on the travel I turn to Kef and I don't puke my heart out. It's more than acceptable for an average consumer. I think it is better than B&W P7, M&D MH40 and only and allmost as good as Audeze Sine. It is very comfortable, looks cool on head and its durable as they get. It's all leather and aluminium. If you can get one. Get this. I've had hundreds of headphones and M500 is one of the few that get a solid 5/5 recommendation from me. It's a fricking lovely headphone!
Audeze Sine
Ok, not exactly what was asked for. But since Sine can be bought for $150 used it's not way off the mark. It is afterall the ultimate on-ear headphone. I think it sounds bit weird on the treble and it's not the most spacious sounding heapdhone but for potential (used) price of $150 it is a solid choice. I know original budget was $50. But heck, stretch it a bit and you got a headphone that is end game for any sane person. It's leather and metal, quality all over. Personally I found it a bit uncomfortable so I can't give it my highest recommendation but fit is of course very personal. If you have the money, go for it. It's better sounding than M500 but not as comfortable. Pick your poison.
Kitsound Milano
Ok, this is a funny one. Don't laugh though. This is a headphone that has a lot of different rebrands. I have exibel version. Best know version is kitsound Milano I think. It's build by some chinese company called vsonic or something. Do some google if you want. That same compady had another on ear built for dick smith. VT-68 if I recall. VT-68 is a decent on ear also, but not good enough to mention here. Anyway this "milano" is insane value. It is built mostly of metal, earpads are soft as they get and cups have this nice rubber coating. Cable is detachable. Most of my headphones come and go but I still have a set of these
It's a warm sounding headphone with plenty of bass and huge soundstage. Soundstage is exceptional for a on ear, perhaps better than on M500 or Sine. These normally sell for like $30 and for that price it's a no brainer. You don't have to settle for that gold color, other rebrands have more mature color choices.
Martin Logan Mikros 90
These things were like the most hyped thing some years ago. And like with most over hyped headphones nobody talks about these anymore. Originally these cost something like $399 but they got discounted to $100 and thats when these became a temporary hit. It is a very good headphone though. I think it is as good or slightly better than Kef M500 and only by a small step behind Audeze Sine. You can grab a used for $50-100. It's really good looking headphone, most of it is built out of metal and covered in leather. I love the design. One of the prettiest headphones I've seen for sure. These have a very dynamic, lively sound with average soundstage and excellent imaging. However the cup swivel is too reactive and it kind of tends to fall out of your head. Clamping force is also very high. These are one of the few headphones I find uncomfortable, and as such I can't really recommend these. It also has issues with earpads falling apart and headband system becoming loose. Shame, it is damn pretty headphone.
Master & Dynamic MH30 and MW50
I'll go against every rule on head-fi and suggest MH30 even though I have not heard one. However I used to have MH40, the big brother. It was a nice, warm and a bit bassy headphone. How master $ dynamic builts their headphones is par none. It's crazy really. Many here have propably owned a headphone that has some stitched leather or something, but when you first touch master & dynamic headphone it is an instant wow factor right there. Way those guys work with leather, the details they engrave in metal. It's crazy. Really, you have to feel it to believe it. MH40 was quite mediocre in the end but if one can get MH30 for less than $100 I'm sure it is a good buy. I had the bluetooth version MW50 which I though was excellent. My head did not agree with the swivell function. Shame, MW50 allmost dethroned M500 .
Msur N350
This headphone is well representive of the value good chi-fi can offer. Wooden headphone that has most parts built mostly out of metal. I can actually wear it as over ear, but it is very discreet looking which is important to me. Truth be told, I don't have that precise memories of how they sound. I still have one though. I'm more familiar with msur N550 which is one of my alltime favorite headphones which you can't buy anywhere these days. N350 has the same drivers. N550 is an absolute killer value for a headphone. Performance wise it is way up there with the likes of Fostex TH-X00 and easily better than bad expensive headphones such as Beyerdynamic T5P, Bowers & Wilkins P9 or Ultrasone Signature Pro. Even though N350 is not at the same level it is much related that the driver tech alone makes it a worthy buy. Beryllium baby!
JVC HA-S400
This is propably one of the most overhyped headphones ever, imo. It's not a bad headphone. It has nice clarity to the sound but it does nothing exceptionally well. I've owned these two or three times and I never quite got the popularity. It surely is better than your random small headphones but I think those Fischer-Audio/Brainwavz headphones easily beat JVC's.
So in conclusion. Go for Audeze Sine if you can up your budget. Save something in the long run as you would allready have an audiophile approved headpone. If that is not an option look for a deal on Kef M500. You can't go wrong with that. If that is not an option go for Msur N350. It has driver tech most major manufacturers only dream about. I hope this was somewhat helpfull