In addition to the great answer by a fellow poster, I would like to add that several of the office supply stores have school supply campaigns where they donate materials to families and schools. STAPLES is especially proactive to help within the local community as well as TARGET.
In addition, I know that garage sales are often a great and cheap resource for school supplies. Sometimes if you discuss your situation sellers will give away their wares or charge a reduced fee.
Many of the activities on Education.com include ingredients or supplies that are commonly found in family households with school-age children, such as crayons, paper, pen/pencil, stapler, scissors, glue, food, magazines, etc.
However, if you come across an activity that you'd really like to do, and are struggling to afford the materials, consider these options...
>Visit your local Walmart or dollar store. They often have art and school supplies that are inexpensive.
>Research if there is a creative re-use center in your area. These are places that recycle materials, including art supplies, and re-sell them at bulk (very inexpensive) rates. Here's an example of one in the SF/Bay Area: http://www.east-bay-depot.org/
>Contact your local churches and/or non-profits: they may have programs that provide free or low-cost school and/or art supplies.
>Host a bake sale, car wash or rummage sale to raise funds for supplies.
>Contact your school's PTA to see if they are interested in hosting a Family Activities Night in which they provide the supplies for families who participate (or get a local sponsor for the supplies).
>Hunt for supplies at garage sales. This is one of my favorite things to do, and I often find piles of stickers, stamps, paper, postcards, etc. for less than $5 (particularly at estate sales where 'everything must go').
I hope these suggestions help, and that you are able to enjoy the activities (and/or worksheets) on Education.com.