For the FM enthusiast, here's a low cost kit option

CANCK108 - Universal FM Transmitter with Mic and Line Inputs (Solder Kit)
"The CK108 offers an FM transmitter that provides both a built-in sensitive microphone and an RCA jack for line input. In the line mode, it can be easily connected to any audio source to broadcast the audio signal to any FM receiver within its range.

6V DC or 4 x “AA” size batteries, frequency adjustable from 88 to 108 MHz. Low power, can be operated under Part 15 of the FCC rules with a short antenna."

Order Page Here: CANCK108 - Universal FM Transmitter with Mic and Line Inputs (Solder Kit), there is a review here, and for more in depth info, see the Set-Up Manual, here.