Just get regular play sand. I think it cost me 3 and change for a 50-lb bag at Home Depot.
As for the lunar lights, I got them off of the Drs. Foster and Smith site:
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3733+12760&pcatid=12760
I have 1 main "hub" and 2 links on the 55 and it looks excellent. They are not on sale now, so if you want a better price, you can wait and see if/when they reduce the price. I think mine were on sale when I got them. Even for full price though, they are great.