I live in an apartment where my neighbor has a sub right next to my wall. It is never too loud, but always just loud enough to irritate me. Sometimes my computer is louder than his sub, but its the constant thumping bass that really gets to me.
To me, it would not be cost effective to isolate my apartment. I would put my money toward studio time, build a vocal booth, and mix in headphones. I spent around $300 building a vocal booth that was not really that isolated, and was hotter than hell on the inside. It sounded alright after cutting all the bass out, but I image to isolate my apartment, it would cost around $8,000 if not a whole lot more. I have a friend who builds houses for a living, he isolated his garage, and it cost him around $12,000, he did a beautiful job though.