I've got a pair of cheap bookshelf monitors (Alesis 3's) that I've grown accustomed to for mixing in the home studio (CHEAP at maybe $100 for the pair). They're not the flattest or the most truthful, but I do this mostly for fun/learning experience and they get me to my goals! I don't have a treated space so I'm more prone to perfecting mixes using multiple sources rather than trying to base everything on one source.

Now I'm at a stage where I'd like to invest in a pair of good, relatively transparent, relatively flat-response open- or semi-open back cans in the $200-and-under range.

I also want to get some decent closed backs for tracking and detail-examination purposes - I'm thinking Sony MDR-7506's as I love these headphones and I dig the bright sound and detail they give... they're so fun to listen to!

I've been looking around at option , and obviously there are hundreds of threads on scores of forums like this, but I'm just looking to get some other stuff on my radar and see what you guys are using, what you've had success with and stuff.

Dave

1st off,
you know not to mix with headphones.
you need trustworthy monitors to mix on.
 
you can check mixes with cans, sure, micro edit, fix phase issues, stuff like that.
but you do not mix on headphones.
 
2nd, if you were to mix on headphones,
you'd need to up your budget by about 5x to get anything close to accurate for mixing on.
 
but like i already said, 
don't mix on headphones.
 
there are lots of nice budget cans to check mixes on,
lots of reviews to read up on:
 
https://www.cnet.com/topics/headphones/best-headphones/
 
https://www.innerfidelity.com/reviews
 
https://www.headphone.com/
 
https://www.head-fi.org/
 
i have and use some akg 240 ii studios to check mixes on, 
they work great,.
 
also uses some Sennheiser CX300 II CX 300 II earbuds, to check and i use them to track.....
work great.
 

Sounds good batsbrew! The 240's have been on my list for a while so I'll go a bit deeper into investigation. The Senn HD 598/600's, AKG 612's and the Beyerdynamic DT 990's all pique my interest a bit too.

Of course after this amount of time I've stopped mixing on headphones - whatever I get will primarily be for checking balance and detail-oriented work while actually mixing. For my uses they've been a good reference to see what other people are going to be hearing when listening to my stuff, haha!

Hopefully somewhere down the road I can afford some "big boy" monitors :D but for the meantime, its serving me pretty well to really learn how my equipment sounds, what its strengths and weaknesses are and how I can work around them to still get a good result.

The Sony MDR-7506s are a solid choice for tracking, and not bad for mixing if absolutely necessary.  I like the way they sound; bright and a bit edgy but still pleasing.  Sound isolation is decent, and they stay comfortable for long sessions.  They're definitely one of my favorite closed-back headphones, and a bargain at about $80.
 
I also have a pair of Sennheiser HD280 Pros.  They go for about $99.  These are very good tracking cans because they have excellent sound isolation.  But I've never been crazy about their sound.  They sound "stuffy" to me.  And they tend to wear tight and get rather uncomfortable after a while.  Some people love them, though.  It's just a matter of taste.

For good mixing, you really want open-back headphones.  I have a pair of Sennheiser HD600s that I adore.  These go for about $285 and are worth every penny.  The open design makes them sound very airy and natural, offering detailed sound throughout the frequency spectrum.  I understand they might be a little out of the budget you mentioned, but they're worth the extra cost, in my opinion.  They're comfortable, lightweight, and accurate.  

While it's true final mixing should usually done on studio monitors, you can get pretty darned close with a set of cans like the HD600s.  

That's a good call Heather, I've been hearing lots of good things out the Senn HD6xx's but until now, I haven't considered them. I think with the amount of trading off I do while mixing - I tend to do probably half of my mixing on headphones, the other half on my monitors - it'd be a good investment! I'll save for another week or two and then give them a try
 
 

If forced to monitor occasionally on headphones here is an option that ties in with headphones. I would download the demo and also determine if the plugin in covers your model.
Uses a webcam to track your head. Adjusts EQ for your model. Does some other panning stuff. Quite cool actually.
https://www.waves.com/plugins/nx#introducing-nx-virtual-mix-room
 
The thing I find interesting is we mix on monitors for people who mostly listen on headphones or we mix on headphones and try to make it seem like monitors so that people can listen to it on headphones. Are we going in circles here? If I were serious about a mix I would make it sound good on both, but lean slightly more toward headphones for obvious reasons. We are way past the late 70's when everyone had two speakers in the living room hooked to a stereo.

Starise
 
The thing I find interesting is we mix on monitors for people who mostly listen on headphones or we mix on headphones and try to make it seem like monitors so that people can listen to it on headphones. Are we going in circles here? 

 
absolutely not,
headphones are the worst, for being all over the map in terms of sonic fingerprints...
the worst.
 
you cannot make good decisions about low end translation on a headphone.
but a good set of monitors will let you make those decisions,
and those decisions will translate on the MOST headphone combinations,
but this never works the other way around.

I would never use headphones for mixing.  To listen to the mix, OK but not for mixing.  
I have some of the headphones previously mentioned and not that fond of the Sony's.  I've got some similarly priced Shure's and they are about the same as the Sony's.  My favorite is an AT ATHM50X for "low price" studio headphones.
 
My take is mix as good as you can get it with studio monitors and others will be good too.  But the right studio monitors.  

fireberd
My take is mix as good as you can get it with studio monitors and others will be good too.  But the right studio monitors.  

 This is what I do. I try to get the best mix on both. 
 
Not trying to be disagreeable here. Comment not directed to anyone in particular. Thinking out loud. They sell headphones made to mix with. Dedicated mixing headphones. If they didn't have some value I don't think they could be marketed as such. If I lived in a small apartment with neighbors, I would likely use mixing headphones more often.
 
It can't be argued the two are different experiences. There is a huge difference in reverb/panning and the like when going between the two. 
 
I much prefer the monitor experience if possible. Sadly, it's more likely to be a cheap pair of ear buds or something similar to Alexa most people likely listen on. Good reason to have a lot of detail in mono.

Sonarworks or Waves NX used with headphones they support can go a long way to resolving most (but not all) of the problems of mixing using headphones. Especially if the monitors are too small to produce deep bass, or the room doesn’t allow for it.

Checking a mix on cheap earbuds is also a good idea because lots of people listen to music that way most, maybe all, of the time. I suggest getting a set of the bog-standard wired Apple ones, they’re the standard issue with all the iOS stuff, and actually aren’t that bad to listen to, unlike the cheap Chinese knock-offs.