Funny enough, I know two separate groups of people doing that. One in an apartment in SF running a shared Wi-Fi network with VLANs so they don't step on each other's frequencies, and another group sharing WISP infrastructure in semi-rural Utah where they can't convince ISPs to lay fiber. (Although I think the second group now uses that as a backup for Starlink.)
Yes, UBNT nanobeam 5ac AC wireless[1] is pretty dirt cheap. Can get a pair for about $199 for a wireless P2P link that can work over several kilometers. I have deployed a number of these myself, along with more high bandwidth airFiber stuff.
