Private Investigators cost about 500-1000 dollars per day.
Recording equipment can cost thousands of dollars.
One method used by private investigators is to collect ecidence illegally, and then they know what eveidence to collect legally, or what issues to pursue.
Workers should find out what they can legally record and collect in the work place. And collect recordings out of habit, not before something happens.
Often you made not know an employment law has been broken until after the fact.