Live sand is very good, complete with the benifical bacteria, and when cycling a tank helps to speed up the process.
It comes down to a matter of grain size
Southdown playsand is calcium carbonate based just like you want from the ocean, also just like some live sand that you get will be. But it also has an excellent amount of appropriate grain size that can't be beat for the price when building a sand bed for your tank whether it be shallow or a deep sand bed.
We also use it as a method to save some money. Build your sandbed with the cheap, calcium based, southdown and seed it with some livesand.
Southdown can run 5 or even 10 dollars a bag for 50 pounds.
Dry sand can cost 20 to 25 dollars or more for 50 pounds at the LFS. Livesand can be even more expensive than the both put together, but you would benifit from some to help seed your sandbed.
Got it
Thomas