I used the quickcrete playsand for the bottom 100'#s. Then I used argonite for the middle/top layer, 80#'s. Then I topped it off with live sand 40#'s. I have a 125 gal tank too...
Cost:
quickcrete $5.58
Argonite $40.00
ls $40.00
Pretty cheap compared to spending on average of $2.00 a # (which would have been $440.00 )
Let's see....$88.00 compared to $440.00....
pretty good deal...