I came across a post in a forum last night where the poster wanted to know if a wireless in-ear setup that cost $600 less than a name brand option would be OK to buy. The answers came pouring back and they were all negative. Not mean, but saying that it would not be a good choice. Quite simply, you get what you pay for.
The poster came back with the thought that it would just be for use with his band that only played small venues. The responses were all to the effect that if RF issues, audio distortion and build quality issues were OK for small venues then he should go right ahead and save himself six hundred bucks.
There are some instances where you are just paying for a name and you can get good performance out of something that costs less. IEMs are not one of those areas. Even if you never encounter RF issues there is so much more to the setup than finding clear radio waves. Cheap construction and inferior circuitry can really ruin your day.
Something I've noticed about the cheaper sets from all manufacturers is that just about the time you get things loud enough for the performer, the limiter kicks in. That's when checking out a single channel. So when you're checking out each channel before the set, it's all making it, but just barely. Once the whole band kicks in, the monitor mix is utterly smashed by the limiter and all the performer can hear is mud. Some of the problem might come from cheap buds, but even very good buds aren't going to make up for an audio chain that can't handle the levels that a professional mixing console is going to throw at it. I've heard of bands turning off the limiters and having a better time of it. Those limiters are there for a reason though. High levels of sound pumped directly into a person's ear canal can have serious consequences.
Then there's the issue of build quality. If six months after you buy it, even with light use, and you find the case coming apart and the left ear dropping out unless you hold the cord just so and tape it down, are you really going to be glad you saved all that cash? Even with warranty replacement, it's still a hassle you don't need. So what do you do?
The best option would be to just save up until you can buy something decent. You should probably disregard the propaganda on manufacturer websites and just ask around and find out from people who own them what will work best. If you don't need bells and whistles, don't pay for them. A lot of makers put the same circuitry in all their models and just enable features on the pricier ones. If that's just not an option, take a look on the used market. Well built audio equipment can be found for significantly less and will often have 80% or more of its service life still ahead of it. If that makes you queasy then going with B stock or open box merch can knock at least ten or twenty percent off.
Don't fall into the trap of getting a starter level piece when it's not what you really need. The philosophy I've always gone with is, "Buy your second one first". If you're going to wind up paying $800 for good IEMs, why add the purchase price and maintenance of a cheap one to the bill? Be a little bit of a gear snob and don't let me catch you saying, "Well... it works." Passing signal and passing good signal are two vastly different concepts Brethren of the Knob and Fader.