I think your choice of topic would mostly depend on your course requirements, expected amounts of efforts involved, etc. In order to give an informal yet still inspiring intriguing Economics presentation, I'd suggest starting with SEVERAL topics that are directly related to the community (school, club, etc.) that you're part of, and pick the one that best fits your purposes. There should be thousands of possible topics for your presentation if you care to connect your economic command with community issues. Examples include the social benefits and opportunity costs of the newly-built student center, the marginal and total effects of rising prices on the profitability of the canteen, and so on. I am sure you will impress your audiences and raise their interest if you incorporate into your presentation your own economic models (just simple ones) with real data and use them to explain your research findings. STATA is an awesome tool in this regard. Good luck! :)