To study overseas in Germany at minimal cost, your best option is to enroll in a public university, as they generally do not charge tuition fees for international students, making education essentially "free"; you can further minimize costs by applying for scholarships offered by the German Academic Exchange Service (DAAD) is a scholarship which can cover living expenses, travel, and even tuition in some cases.

If you want to pursue research after 12th with a background in Physics, Chemistry, and Biology (PCB), you can consider a five-year BS-MS dual degree program at IISc, IISERs, or NISER. In your first year, you'll need to take all four subjects, including maths, physics, chemistry, and biology. You can specialize in your subject in your second or third year. After completing your course you can apply directly to your preferred institute.