| There are transmitter packs available which plug into regular mic's but they tend to be more expensive than just getting an all-in-one mic with built in transmitter. They're a single unit, and aren't detatchabe.
If you really want to hang on to your mic's you could go with a guitar transmitter/belt pack. Most of these have mini-xlr's as inputs, you so you can get an xlr-minixlr adaptor cable, and plug a mic in to the guitar transmitter. It's up to you if you think this is an appropriate solution (I think it looks OK - you still have a cable, but just running to your belt, so you can't trip over it). I've done this as a backup/experiment, and it works fine.
Ian | 
