How are you trying to use them? We have several sets of Sennheiser hand-held wireless microphones that work well for what they are designed to do - pick up spoken words from someone holding them a few centimetres in front of their mouths. They are around £100 a set and seem to be able to take a few knocks and being rolled around on the floor a bit. They are not designed, however, to pick up sound from all-round, and they can't really handle the higher notes from a properly trained snging voice. It's probably worth getting a stage lighting / audio company in that can properly advise you (searching for "theatrical chandlers" might work, too) and be clear about what you want your microphones to be able to do. We use Wizard Lighting in Woking, who are excellent, but probably not the right area of the country for you.