It doesn't have to be that large. Many people have "personal" ASNs.
Check out this blog (not me, I just remember it from years back): https://blog.thelifeofkenneth.com/2017/11/creating-autonomou...
Check out this blog (not me, I just remember it from years back): https://blog.thelifeofkenneth.com/2017/11/creating-autonomou...