Personal computer (laptop), as a radio station?

Good day to all!

There was a question about the acquisition of FM-transmitter for PC. Yes, yes, it is for a personal computer.

The question arose with the aim of organizing audio transmission from a laptop to an audio system that does not support MP3.

In fact, a convenient thing is included in the computer, you yourself are in any room and your favorite music is with you, at least from an MP3 player (from the radio), at least on any old stationary tape recorder (if only it supports the FM band).
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Unfortunately, searches in RuNet have come to nothing - a very large selection of automotive modulators, but for an ordinary PC there is no.

So far, all I could find (not advertising):
Griffin RocketFM / FM Transmitter for Mac and PC Computers - $ 59.99 (!!!)
Wireless USB Audio FM Transmitter for PC / Laptop / MACBOOK - $ 31.55

UPD> Found and in RuNet: Belkin Tunecast II FM-transmitter - 880 rubles. But it looks cumbersome for a laptop - it will be inconvenient to carry around.

I looked like a good one.

So, the question arose. Why such high prices?

Although I do not really understand the radio equipment, but soldering a device that removes sound from the audio output of a sound card (jack 3.5 mm) and broadcasts it at a given frequency (albeit stitched in the device) is not that expensive?

Someone else was interested in this topic? Tell me, please, are there any ready-made solutions?