You’re probably right, but I don’t have sufficient knowledge in this area to confirm. Wikipedia’s Channel 3/4 article doesn’t say anything about frequency vs. costs.
Note that the data rate of video vs. audio is much, much greater. So very low powered unlicensed (audio) signals over AM or FM are allowed in places like the US. (Those licensed school lower power stations are at the level of a 9 volt battery, IIRC, so scale that down.) Here’s a summary of FCC limits on unlicensed broadcasting within various bands.
Note that the TV band is more strongly controlled. Definitely no DIY TV broadcasting there.
Video requires so much bandwidth that in order to get a signal to go any useful distance at normal broadcast frequencies you have to produce a lot more power.
The 2nd post by the OP mentions WiFi ranges. There, you can transmit decent video streams using standard WiFi devices since the frequency is so much higher. Lots of useful bandwidth per channel.
So there are many commercial devices that take an Internet stream, wireless if need be, and convert them into a signal that can be watched on a TV. E.g., some Rokus.
But the OP’s 2nd post is still muddled and I cannot offer any specific help.
(BTW, I’ve owned some early VCRs that were channel 2/3.)