What you are looking for is "tropical play sand" that has been sterilized. I have had Southdown and really this is all it is.
Go to a smaller greenhouse, plant, feed supply store and ask if they have tropical play sand. Souther States Coop, here in the carolinas carries it and most other high end top supplies. THe larger stores carry the cheeper play sand that is quartz based. The tropical play sand is coral-based, whiter and very fine.
Be sure to wash it a number of times to get the extremely fine material out. Also, having a magnum with a micron filter handy does a great job of clearing the water afterwards. I set up a new 75 gallon just last yesterday and the water is clear and my 3" deep sand bed cost $15.
I know this stuff is fine because I have set-up 3 tanks with this type of sand and fish have always been fine. Most recently my trigger fish digs quite a bit in it looking for small creatures.
