Our standard projects have a minimum materials cost of $100, with no formal maximum. However, when creating a new project, it's important to keep in mind the less expensive a project is, the more likely it is to be funded. The majority of projects under $400 are fully-funded within 3 months, while projects costing over $1,000 have a much lower success rate.
If your project resources total over $1,000, find a way to break up your request into 2-3 related projects (i.e., "Nonfiction Books Needed for Our Classroom Library “and "Fiction Books Galore! Help Build Our Classroom Library" -- or just give your project titles a Part 1 and Part 2 addendum). This way, your students still benefit from materials even if just one of your projects is funded.
See here for some inspiration for successful low cost projects!