I used to use playsand when I had uromastyxs. I would also have large rocks burried hafway in the sand so they can get away from the sand when they wanted to and the rocks made great basking spots.
Sift the playsand well to get all the small rocks and stuff out of it.
I used to put a bowl of bird seed in their cage sometimes. they liked to eat it once in a while. I never used it as a substrate though. I would think it might be hard to keep clean?
quickcreat makes sand that is baked, kiln dried, and then sifted. its like 4.50 for a 50lb bag. thats what i use, and i dont have any problems. i also put a bowl of finch bird seed in next to there food bowl.