I've currently got my guy on aspen as well. Doesn't cost much, but it doesn't look cheap. Plus it's easy to find. However, I'm more than likely going to switch over to coconut husk soon so I only have to buy one kind of bedding when I go to the store (I use the coco husk for my cresties, and since it works for BP's I don't see why not. I like the smell)
le edit: Forgot to mention that Koga will move the aspen all over his tank. It's completely bare in some spots, and piled up in others. So if your snakes like to burrow, aspen is the way to go.