Search tuned vehicle for pizza driver

Hey people are new here and introduce myself briefly: My name is Johannes, I am 21 years old and I am a student. As a side job I started with a pizza service as a private car driver, because I also know the owners. I get a fixed hourly wage and for each order 50 cent fuel money. So if I drive 3 deliveries at once 1.50 Euro. I took over my mother’s car, a 16 year old 4 year old golf. Since the work there can be stressful and you must quickly from A to B is I work about 3 times a week and drive in a shift around 100 km. Now I am looking for a new car that consumes less. Unfortunately, I am in the conflict that the newer cars are much more economical, but the wear is then relatively high. If the car is old, what it should be for this job, it consumes more fuel. So in good German: I am looking for a car b can you give me tips? Thank you very much in advance!