With a starting capital of 300,000 Ethiopian birr, you could consider starting a small-scale import-export business. This could involve sourcing goods locally or internationally and selling them to local markets or online. Another idea could be investing in a small-scale food processing business, such as making and selling packaged snacks or beverages, which have a steady demand in various marketplaces. Both options could provide opportunities for growth and profitability with careful planning and execution.