A few other issues,
Although you are correct that flight recorders are equipped with a locator device, this device is sonar based. It needs to be immersed in water to operate. If a radio type locator was developed, it would more than likely require much more power to be effective which means more battery power, and more compexity.
Flight Recorders often do not come away from crashes "unscathed". The vast majority involved in serious crashes sustain alot of damage. Of course the recording medium is protected in it's own container and it has to be carefully removed from the mangled case.
If you wanted to develop a floating flight recorder, you'd have to come up with a means to ensure that the recorder would be ejected clear of the wreckage, then protect the entire unit from damage, including the transmitter and floatation device. Remember the average flight recorder weighs over 20 pounds.