sand is ok
I have been keeping snakes and lizards for ten years or so. For the last few years I have been using normal sand (silver sand or playground sand) with no trouble. My snakes all shed OK, and the humidity issue does not seem to apply. They VERY occasionally sit in the water bowl for a day or so, which is fairly normal, and both eat really well.
To minimise ingestion of sand, I feed them both on a large flat rock in their tank. They will sometimes move off this when feeding, but this does not cause any problems.
I believe their wild habitats include sandy (semi-desert) regions, so I shouldn't worry too much about using sand. It's a lot cheaper than aspen (although I STILL don't know what aspen is...).
Cheers.
Pete