Personally, I REALLY like shredded newspaper. Its very cheap (free) and if you put it through a paper shredder it looks good.
I am using a "strip cut" paper shredder that is working very well for me. The alternative is a "confetti cut", which I have not tried.
I hate to pay for a substrate that I will be throwing away once a week or so. The sand needs a lot of work and is very expensive. You can't scoop up EVERY flake of skin and piece of feces out of the sand. I would rather throw away ALL the substrate every week or so and keep a sanitized enviroment.
I know out in the wild it is not sanitized, but these are not wild snakes.
Just my opinion.