If you want a good PBL for your kiddos, this is about starting a lemonade stand. Before starting the project, you may choose to read the book The Lemonade War to your students (I have a resource in my store for this book). I did this activity as an end to our novel study.
This project contains math, writing, critical thinking, problem solving, research, and presentation. If you have any questions, please feel free to ask.
This resource also includes different levels of tasks (depending on the grade level you teach).