Sadly choices in that price range are going to be very limited. The only solid under $600 one I’ve used is the RodeLink at $399 https://www.amazon.com/gp/aw/d/B075KN82NK/ref=mp_s_a_1_5?ie=UTF8&qid=1509638899&sr=8-5&pi=AC_SX236_SY340_QL65&keywords=rode+wireless+lavalier+microphone&dpPl=1&dpID=418-OPKxUdL&ref=plSrch.

All of the cheap wireless lavs I’ve tried in the $100 range are garbage. Saramonic makes one with 2 mics and 1 receiver for $400 I believe, had high hopes for that one but ended up returning because the battery life was horrible. Even if you find a cheap one with decent sound it will almost always only have 1 or 2 channel and you don’t want to be stuck filming a wedding and getting interference and only having 2 channels to select from. Another option is to get a zoom recorder and lav mic and then sync up your audio while editing. Lots of shooters swear by this option but personally I like wireless so I can actually hear what’s being picked up while shooting.