I used to use pine shavings before i knew of the dangers and that my rats had a very bad reaction to it and are still living with it almost a year now.

I use cut up cardboard and aspen cost me around £50 for month mixed together they last about 3-4 months.

Ive heard MegaZorb is good i can get you a link where its just £5 plus P&P for a large bag, ill be changing over to it soon.