Whats a good medium to low budget lav mic.
Define "Low Budget".
The mic itself can range anywhere from $25 to $1,000.
The wireless trans/rec system can be anywhere from $150 to $8,000 (or more).
Those prices are for each individual system, and you will most probably need at least two.
When you get into budget gear there are a number of trade-offs, especially with wireless systems.
As you drop in the price of the mic you get decreased frequency range, more susceptibility to breakage (usually from sweat) and they are generally larger and harder to hide.
As you drop in the price the wireless system becomes more prone to drop-outs, RF interference and decreased range.