There are plenty of different topics commerce students could work on for their project, ranging from things like giving a brief introduction to macroeconomics or microeconomics, or more specific subjects like laws regarding Income Tax or Corporation Tax.
You could pose them a list like this, and have each choose one to work on:
1. Corporate Finance
2. Income Tax
3. Macroeconomics
4. Microeconomics
5. Auditing
6. E-Commerce
7. Managing Data
Any of these titles would be a great starting point for your commerce students to then develop, allowing them to choose how they approach the subject so that all the projects are different.
To help make things interesting, you could also show them a video like this that contends the issue of Income Law, encouraging them to do their own detailed research into the matter for their project.