I recently purchased a heavy bag and floor stand. Instructions say that you just place three 25 pound round olympic weights on the three vertical weight poles. I found that it takes about 350 pounds of weight to stop the stand from dancing around the room. I have a good portion of my barbell weights sitting on my bag stand. Now, I'm going to spend a small fortune on weights. I've considered sand bags, but their flexible nature makes them less than ideal. Any ideas as to an economical weight system?