This maybe isn't the most "green" solution, but I went to a local gun shop and bought a 40lb bag of lead shot and mixed it with some kitty litter (about 80 LS/20 Kitty) and it has worked great. Everything is sealed up nice and tight and wow are they dense.
It was around $40 a bag if memory serves me correct.
I am using these 28" stands from Audio Advisor http://www.audioadvisor.com/prodinfo.asp?number=PGDS400&variation=24