The CVR has an area mike that we use to tell all sorts of stuff. The blade passages mark the rpm, and the sounds of engine tell its power (N1 speed shreeks a bit). The crew also say things, and the timing of the sounds to ATC chatter mark the position when things went bad (when the radar traces are also gotten).
The cost is because they demand that the things run in boiling oil and fall from 1 zillion feet, but new small solid state recorders should be uch cheaper. I would think a light, less well protected one could be built for light helos, if we all thought hard about it.