Well, I would say that most headphones I heard are placed in 3 categories:
0 - 250 $ - entry level, all have a similar level of detail and resolution, regardless of signature
250 - 400$ - mid
400 - 700$ - high end
Everything above would already be summit fi, the sound becomes further refined and usually has some more resolution.
I will immediately jump on a product and yell that it has an awesome resolution and sound if it has, especially if it is priced better, but so far all the products I tested, even those that were called //wonder products for their price// were pretty much wonderful for their price, but no 100$ or 200$ IEM has the resolution of 500$ - 600$ ones.
I found 600$ headphones, a single pair, but did find it, that has the resolution of a 2000$ and above headphones. Its review is in writing right now, the signature is reminiscient of HD800S and that one really surprised me, sounded waaaaay good. But that would be it when it comes to what companies did at more accesible prices.
I don't blame them though, since this is probably a bit of a niche, they need to have enough to fund proper R&D, so they might be placing higher price tags to have how to propel their research forward.
This is strictly for headphones and IEMs since I tested and am testing many of those. I cannot comment on all DAPs out there since I have tested a few and all impressed me, but the differences were not as big as they are between different headphones. A 250$ DAP like HiFiMAN Megamini is quite good sounding actually, DAPs tend to be really good even at moderate prices.