Hi Joe,
We work with a band that has a pretty simple system that works really well for them and didn't require a ton of investment. Very similar to what others have recommended here, and for good reason - it's simple, flexible, and easy to set-up/run.
- 1x 8U deep case - something like an EWI shock-mount case
- 1x Behringer XR18 AIR digital mixer
- 1x Furman power supply (rack mount)
- 1x Seismic Rack Mountable 16-channel splitter snake with 5' and 30' tails
- 1x Apple Airport Express (router)
- 4x Behringer P1 IEM monitor box
- 4x Short XLRM to XLRF cables
They have the splitter snake panel at the bottom of the rack, and the Furman and XR18 are at the top. The Airport is mounted inside of the case with a small bracket. They also put-in a work drawer to hold their IEM receivers (they use wireless)...
The band uses their tablets to connect to the Apple Airport Express and they each run an instance of the XR application. They can then control their own mixes (Drummer = Aux 1, Singer = Aux 2, Guitar A = Aux 3, Guitar B = Aux 4, Keys = Aux 5, Bass = Aux 6, etc).
It's a relatively low cost of entry with this set-up, and should you at some point decide to go wireless with your IEM, you'll have room in the rack to mount a few transmitters.
For the total investment (around $1k if you shop around and buy smart), you'd be hard-pressed to beat this set-up. It's not world-class, but will likely work well for you.
I should also add... you probably don't want the IEM box on your pedal board, because you'd need a really long headphone cable, and that's more likely to get tangled/stepped-on/pulled-out/etc than a positive-locking XLR. I'd hang the IEM box on my belt and run the XLR output from the XR18 to the P1.