Cheapest live sand if from fellow reefers on forums like Manhattan Reef !!!
As far as dry sand, if it is reef safe it's fine. The problem, is you have to make sure it's good. For example. In my previous life before keeping reefs, I used crushed coral. While this won't kill corals, criters and other live stock like live sand because it is better for them to dig, etc.
Now, if it is dry sand that was live sand ( just sitting out of a reef tank), then, I would probably like to cycle it first, to make sure there won't be a cycle in an existing tank and cause harm to animals and fish.
If you do get sand that is not live, it's easy to make it live sand. Just get a cup or 2 of live sand from a fellow reefer and mix it in to the tank, and the dead sand, should become live ( meaning bacteria), will replenish it in a short time.
In the past, I use to replenish my live sand bed, every 6 months with a cup of live sand from the LFS to keep up beneficial bacteria.The idea is if you were paying a premium for live sand, it is not necessary to purchase all live sand ( you can just get a small amount ) and place it in tank ( make sure you don't put in in too fast to blow on corals).