IMHO - there's no such thing as budget IEM's?
Is your $500 budget per band member or ?
What are you trying to accomplish... Wired or Wireless ??? Big cost differential. Whether you go wired or wireless, there's two basic configs.
1. Basic IEM's - mix run from Aux feeds on console - either FOH or stage.
2. Basic IEM's - individual mix control ? (Aviom, Hearback, Behringer)
We tried 1. above - miserable.. no control, and signalling FOH for adjustments was a joke. We then tried a modified version with snake splitter on stage into stage mixer (we have a spare 16-ch Mixwiz) then 6 mixes out to headphone amps with compressor/limiter in between. It "worked" but it was wired, and less than ideal and required much extra time to set up and "tweak" the mix for each venue (eq on console, levels, gain, etc.)
So.... after much research, and since we're a "working" band, gigging Fri/Sat EVERY week, we recently bought INTO the Behringer PM system (P16-I $399, P16-M $199). Been using it for about a month now, and it's as good as the Aviom system I use at church on Sundays, for 1/4 the cost !!!!
The P16-I takes 16-ch's from your mixer (mixer needs inserts of direct out on each ch). You then use CAT-5/6 cable from P16-I to a P16-M on stage. Each of the 6 CAT-5 outs on front of the P16-I will power a single P16-M. Power DOES NOT not daisy-chain between units, but audio will. You can daisy-chain up to 8 of them if IIRC. Each P16-M comes with the usual wal-wart power supply.
Each band member using these (half still use stage monitors) has individual mix control of 16-ch. You can go direct from there to cans, buds or to a wireless unit as P16-M has stereo/mono and headphone out. Also has built-in limiter and tone controls for each ch. Great $$ value.
I go STEREO out of the P16-M into a Carvin's EM900 wireless unit -I do not use the included buds. Have my own custom molds. I also play wireless (L6 G-90) so I'm totally wireless. Gotta monitor battery use tho'
So, decide if you want *wireless*
IEM's or not; how you plan to get the mix to each member, then figure in associated costs.
Even basic wireless for 4-piece band is going to run around (eg: Carvin EM9000) $1600. Go up in quality, and your costs go up accordingly. Add in separate buds, molds, distribution system and you can quickly get into many THOUSANDS of $$$.
We spent $1000 on the Behringer system P16-I, 3 * P16-M's.
I have the Carvin EM900 ($400), other 2 already had their IEM's, and we bought some CAT-5 cables ($50). Total outlay was roughly $2K.
Hope this was useful!!