This is of course a fiery topic that has no correct answer but... When I was setting up my tank I read a great deal on the topic. The prime argument for aragonite is its Ph buffering capabilities, and equally important, its roundish shape for the critters that burrow in it. You are considering 3 choices here
Playsand: this is possible if you can get sand that does not have oil added to it to keep the dust down. To do this you really have to go to silica sand that is intended for a pool filter. It is about 20 bucks for 25KG when you get this kind (that is the best price I could find). Good points cheaper, inert; bad points no buffering ability, it has a rough shape and is a brownish color
Sand blasting sand: This is a better choice. I found some soda glass that was used for sand blasting at about the same price 18 bucks for 25 KG. Good points white, inert and cheaper. Bad points ; no buffering ability, rough shape and not uniform in size (unless you get the certified size which is more expensive).
Peen Beads: This is the choice I like best, is 20 bucks for 25 Kg and it looks like sand... plus if you pick a size from #6-#10 it doesnt float around. Bad points; no buffering ability, good points; looks good and is generally round. It is about the same price. This was recommend in a thread by R. Shimek
I added all three. The silica sand on the very bottom (about ½ inch), 3 inches of mixed peen and beads and about ½ inch aragonite. After almost 4 months it is covered in diatoms and who can tell which is which
