Rabbit pellets have been a great substrate for my purposes.
They are great to burrow in, they clump like cat litter when defecated upon, they are cheap, and best of all, they are safe if ingested.
The two biggest problems with them is that they can get moldy if in a humid environment and they can be drying to particular species of snakes, meaning, they can draw out moisture and cause shed problems if a moist hide is not present. This is why I no longer use them for our Ball Pythons, Mandarin Rats or South American Hogs, due to shedding issues. But our Western Hogs, Kingsnakes and Corns all do very well on them and they rarely have any shed issues.
While I won't say that rabbit pellets are for everyone or for every species of snake, I would suggest that they are worthy of experimenting with and they are definitely safe as I have a kingsnake that I've kept almost exclusively on rabbit pellets for over 15 years and she's still doing well, albeit rather old and slow.
Also, buy them at a feed store rather than a pet store as they are far cheaper at a feed store. If you witness any bugs or beetles coming from them, switch brands or stores as I had this problem for a while when I was buying bags from a certain store and the problem went away after I started buying them from somewhere else.