I stumbled upon a brilliant and cheap product a fair while back which is marketed at kitty litter. It's old newspapers that have been shreded and soaked and then pressed into pellets the size of chicken or rabbit food. It's recycled (I like that environmental factor), unbleached, has no purfumes or additives and is cheap, cheap, cheap!!! The snakes do well on it and can burrow a bit through it although it doesn't tunnel up like aspen and it clumps and absorbs the moisture from the poops really well and makes them easy to scoop up.
For the Swedes here, it's called 'Katt toa-lätt' and I pay 150kr for a 55 litre sack.