What economical ways exist to dampen floor vibration on top floor apartment?
You need something to absorb the movement and vibrations.  

I am not really sure about the layout but you need something along the adjoining wall that is very heavy and won't make noise.  I had the same situation when I was in college and I brought in a large concrete outdoor bench and put a rubber mat under it.  It weighed a good 400-500 pounds and I had energy to move these things back then.  It worked great.

So very heavy furniture plus padding... You could also talk to the landlord and see if he can secure the joists better underneath to see if that helps.