Just a different line of thought here... and might not cost much:
When I was a grad student a few years back, one of the professors of Neurophysiology, who had an awesome lab, needed to isolate all his gear from all kinds of background hum - 60Hz/vibrations etc while doing nerve and muscle studies. He would always use Tennis balls, partially cracked open, just like we would use vibrapods. And it was very effective. I was amazed then seeing yellow tennis balls (probably used) under under machines which cost a lot of money!! I am much more amazed now, looking back at that strategy... I might even give it a shot one of these days.