Two words: PHONE BOOKS. They're horribly messy and the scraps get everywhere, but Sugar loves them! I got him some plastic teething keys for $.29 at a thrift store. Make sure they're solid plastic with no soft or water-filled parts.
You can find cheap thrift store baskets in lieu of expensive chew toys, but you have to be careful checking for glue, paint, or any sort of glaze. Bunnies love hard cat toys and bird toys...avoid any with beads or other small removable parts.
I bought Sugar a plush carrot, and he's never chewed on it, so plush toys may be an option (again, without eyes or anything else chewable). Check it from time to time to make sure the stuffing isn't being ingested.
Any sort of small- to medium-sized box is ideal, whatever is big enough to fit your bunny...they play, chew on, and sleep in them. I work at a dry cleaner, so I bring home the long boxes used to ship rolls of plastic bags. Sugar doesn't know they're free, since they work just as well at the $24.99 sleep houses at pet stores (better, actually, since the store-bought houses are too small for him!).