The range of my FM transmitter is over 2km to my very sensitive home stereo tuner or to my very sensitive car radio with the antennas 80cm long and parallel and over a large river valley so that there is nothing in between. Its range is about 300m to my cheap Sony Walkman portable radio. Its range is across the street to a cheap clock radio or a $1.00 "radio" from the dollar Store.
It has a voltage regulator so its preamp works fine when the battery is new or old, and so that the radio frequency doesn't change as the battery voltage runs down.
It has an RF amplifier for extended range and to isolate the antenna from the tuned LC circuit.
It has pre-emphasis (treble frequencies boost) so that it sounds perfect like a real FM radio station.
A 9V alkaline battery will power it for about 4 hours but the range will keep dropping as the battery runs down.