I have the cheapest UE5's from Ultimate Ear's.
But here is my theory behind in-ear monitors: they are primarily for monitoring. When I'm in a band situation, I'm only concerned about hearing the click, the track, and whether or not I'm in tune when I'm singing with the band. Why I would need anything more expensive than the $399 UE's is beyond me. Bermuda here has some pretty pricey ones, and I'm sure there's some kind of aural difference between two drivers and more than six drivers, but when I look at what I need to hear, the UE4/5's are fine.
Advice: if you get regular ones (no vent), you essentially can't hear anything that isn't coming to you through the in-ears. So be prepared to ask the band to all go through the mixer. If you get the vented ones, you might be able to hear other things around you that aren't going through the system, but then to me, what's the point of getting in-ears? You could get that with a wedge floor monitors.