Monahan Paper in Oakland (510-835-4670) cheapest cardboard supplier in the East Bay:
OR, you can collect cardboard from Costco, bicycle or furniture shops, or other
businesses.
Here are sizes and costs of rolls of (thin) cardboard from Monahan:
36" x 250' 750 sq. feet $40 34lb
48" x250' 1000 sq. feet $52 53lb
60" x 250' 1250 sq. feet $70 65lb
72" x 250' 1500 sq. feet $80 78lb
Monahan has a $170.00 minimum for prepaid delivery and a $4.00 fuel charge. If the
minimum is not met then there would be a $8.00 service charge.
Always call ahead of time, as they might need to order your materials.