An electric bike is the undisputed champion when it comes to the ratio of earnings to operational expenses.
Compared to a regular bicycle, you don't get physically exhausted, meaning you can ride 2-3 times more kilometers per shift, complete significantly more deliveries, and preserve your energy and health.
Compared to a car, you don't have to deal with high fuel prices, stand in Warsaw's heavy traffic jams, waste time searching for parking spaces near busy restaurants, or worry about expensive parking tickets. The rental price pays for itself in literally a single shift.