I think you have an opportunity to teach 2 things w this project. 1) the obvious....the sewing project, and 2) have them keep a record of their materials and costs. Then discuss expenses and cost-cutting ideas, etc. (this could include borrowing tools as opposed to buying them, sharing tools, the source of the fabric..gifted , thrift store, WalMart, LQS.)
Many young people don't get this sort of experience at home or school.