A good source for carbon rods (or tubes, both are available) is
Composite Structures Technology in Tehachapi, CA, website
http://www.cstsales.com You will have to call their ordering number to
place an order. Ask for a student discount and explain that you're
doing a school science project. Matt and Gail Gewain, the owners,
are good people.
If you can get by with wooden dowels, that would really cut your
costs.
Peter Young