Fabric stores may have fabric ends or cardboard bolts they would be happy to donate. Local libraries often sell used books for as little as fifty cents. Most hold free story times or will offer to have a librarian bring the wonderful world of books to your kids. Some utility companies, airlines, children's societies have free learn and colour books for children. Call and order as many as you need.
Video stores offer free rentals on community based videos like streetproofing, etc.
Ask the staff to show you their free rental section. Contact your local early childhood teaching facility for volunteers for your centre. Often parents know of a retired person who would be more than happy to read to the children, teach a craft, music lesson, dance, etc. Put the recruitment word out to your parents. Place a free ad in the local bargain newspaper for used computers for your kids.