Interesting transmitter on 420-480 MHz
I experimented a little with VCO from Nokia phone (R0464), added an RF amplifier and a microphone. The range of this fm bug is up to 1km with full CR2032 battery and good conditions. As the battery discharges, the range s as well as the TX frequency. The bug can be received at a frequency of around 430 MHz and that depends on the battery voltage.