Here's a post I made to a similar thread a week or two ago, slightly edited. Maybe it will help.
Doing the wireless thing with any sort of reliability over the long term is an expensive and, at times frustrating, experience. Basically, the rule in wireless is "you get what you pay for". Yes, you can get occasional good results with cheap equipment. But, if you want consistently good performance, you're really going to have to come off your wallet.
If it were me, the only two names out there are Shure and Sennheiser. Yes again, there are cheaper players, but they won't have the reputations of the big 2, and there's a reason for that.
They both offer systems that will do 4 channels in one rack space, and they might offer 8-channel units (I don't know). However, they are very expensive, several thousands of dollars. Also, even if you use a combined multichannel system, you may have to invest in an antenna combiner, which will cost several thousands more.
Beyond making the big spend, there is also the hassle of managing and coordinating the frequencies they will use. Each IEM unit, even in a combined unit, needs its own frequency. However, picking out frequencies is not as easy as just dialing in the first several frequencies on the dials. Before you purchase, you have to consider which band is going to best for you in terms of frequency availability and performance characteristics in the areas you'll be using the system. And then, after you purchase, you have to contend with interference issues from other operators on those same frequencies in the shared spectrum as well as from other electronic devices. These will change from venue to venue, and from city to city. You can even get interference from you own devices. Moreover, you will be at the mercy of laws and regulations regarding their use... and these change from time to time... and has resulted in wireless systems instantly turning into very expensive pumpkins because a rule change made those that operate on certain frequency bands illegal to use.
On top of all that fun stuff, you also have to manage the expensive belt packs and the antennas and batteries that come with them. And, since we all know that if guitarists and drummers can't eat something, they'll lose it or break it instead, you better have extra packs, batteries, and antennas on hand, and be prepared to spend a good amount of time maintaining them and teaching/reteaching everyone how to use them and not abuse them.
Dumping a single mix into all your IEMs is a way you could get your cost on a wireless system down... you'd still need at least 5 belt packs, but at least you'd only need one transmitter and you wouldn't need an antenna combiner. But, keep in mind that in this sort of setup each member won't have individual control over their monitor mixes. And I would definitely avoid the temptation to just dump your house mix into the monitors. This is because it won't be tailored to your ears, it will be tailored to the venues... tuned to the spaces, and so it will change from venue to venue. Definitely not a good way to achieve good quality and consistency in your monitors... and kinda defeats the purpose of spending all that money on a reliable wireless monitor rig.
You will still need your own mixer to bring in the instrument and mic sends and send them to the monitor channels. If you'll be touring with this rig, you probably won't be handling your own FOH mix. So, you should also have some kind of way to split the instrument/mic sends off to the FOH board, many times this is done by way of a splitter snake. This will add to the cost of your rig as well.
There are also outfits out there that'll build you a portable IEM system from components. BTPA is one, and there are others. They have demo videos up on youtube. I'm sure they aren't cheap either... but isn't that always the way in this business? Also, check out the rig-building videos put up by Riffs, Beards & Gear and others... this might make you feel good about a DYI'ing it and help save you some bread.
