[jiveturkey]

You're most likely overthinking it.

For your use case, you are primarily concerned with fireblocks. They are unlikely to exist in an older home. They can be detected with a simple stud finder, which range from $30 for the simple (good enough) kind, to $1000 for the radar kind. Simply knocking on the wall is also good for this purpose.

You likely have pretty fixed locations where you want the wires to exit into the room, so you can run a borescope through those places. These are also pretty inexpensive.