I was half interested in putting a ballistic insert in a backpack I carry at work, but the price for something that, in the highly unlikely event I would need it, wouldn’t be on me or near me seemed prohibitive. But browsing ebay and gunbroker, I scored an out of date pair of Level II inserts for less than $80 shipped. I like arts and crafts, so going to cut them to fit, and sew the covers back on, to fit the two bags I carry most.
Anyway, you can get piles of out of date, but still perfectly good soft ballistic inserts on ebay or gunbroker and line the back of a sofa, or some other well placed piece of furniture in your home, depending on it’s layout, and whether or not it would be useful for you when you need to repel boarders. If this was a big concern for me where I lived, and it isn’t, I would rather depend on something designed to stop bullets, rather than say books. I look at my book sheves and there are a lot of very large gaps in coverage.
I do work in a violent neighborhood, and have treated the victims of drive by shootings. I have thought quite a bit about what I would do if I lived in that neighborhood in a clap board mill house.