Price has less to do with it. What I meant was that for example if you're using a decent smartphone with the proper apps, you can go ahead and get as much as a $1,000 CIEM if you want to as long as for example it has a neutral response (no artificial bass boost that might need a real amp to control properly), well over 110db@1mW sensitivity rating, isolates well, and impedance doesn't swing wildly off the nominal rating of preferably near 32ohm (a little bit higher is likely better than 16ohm), then the 5mW at 0.1% THD of a smartphone's integrated DAC-HPamp chip won't have a hard time driving it and ergo you can enjoy much of what such an IEM will have to offer.
The problem there is that fullrange response, very neutral response especially from a single driver and/or smooth transition between multiple drivers, load stability, efficiency and low distortion, and low price don't always go together in equal amounts. Generally however most IEMs are efficient enough and even multiple-driver designs don't tend to cause the same amount of impedance swings as with many multiple-driver speakers. In any case, you have to do your research - going up to a $300 IEM might not be that much more over the $200 IEM (well, depending on which $200 and $300 IEMs) to start with, and then depending on which $300 IEM it is, your player (assuming it isn't, say, an X3 or DX50, and is a subsidized $200 cash out smartphone) might end up inadequate for driving it.
So really what it comes down to is what gears are you referring to, because a lot of parameters may be at play there.