I tried cypress mulch once. It was wet, and I discarded the bag. Wet substrate encourages various opportunistic, naturally occurring species of bacteria which can produce skin diseases in snakes.

My own substrate of choice is several sheets of newspaper with a hiding box for minimizing burrowing. As far as I know, both aspen and shredded newspaper are acceptable bedding materials. Kitty litter is absolutely unacceptable, in my opinion. I once opened a kingsnake that strangled on an inhaled piece of kitty litter.

Try calling a farm supply of poultry feed store in your area and see what sort of litter they sell. Prices ought to be better than Pet Smart.

Good luck.