Teachers can find a wealth of grade-appropriate lesson plans online. Experiences and caring teachers post these by subject and grade level, and many of them are excellent. Feel free to borrow, adapt and improve these plans according to your students' needs.
Organizations offer a wide variety of resources for teachers. These can range from national associations to local chapters of the teachers' union. Some organizations even offer free technology for the classroom. A little searching online will yield more sources than you can possibly take advantage of. Start with your union, then expand to your teacher associations.
The online teacher community is strong, and many teachers are generous with leads to resources and are actual resources themselves. Join chat rooms, forums and organizations formed by teachers online, and you will be inundated with resources.
Libraries are eager to loan teachers materials. The Library of Congress even makes much of its collection available for free online. Many local libraries have teacher membership cards that allow teachers to order books and have them delivered. Be sure you are utilizing all your library's resources, and befriend your local reference librarian.
Many Internet sites--such as donorschoose.org--will raise money for the resources you need. Simply write a proposal, and a donor may decide to buy what you need and ship it to your school. The site will verify your status with the school.