
Some places stock a newspaper-based bedding, it's basically little squares of newspaper. There's a couple places near me that sell it - very cheap too, about £3 for a huge bale. The only downside is the papers they use - sometimes print can run off and you end up with bunnies with grey feet!
Personally I use Yesterday's News for my little furries, but I don't know how economical that would be for you - I buy the biggest bag at £9.99, and it covers about 24 square feet. Very, very absorbent, not very soft though; but small enough pellets not to cause discomfort. Safe if the rabbits munch it too.