Gravity is a much more reliable force than electricity and requires little maintenance. It still works when the power lines are down. If you can meet the grade requirements, gravity is the way to go. Grades can often be flatter for outdoor piping, not the standard 1/4" per foot used inside buildings.
I would work with 45 degree turns rather than 90s if possible, and don't forget cleanouts. It is possible to turn pipe in a long sweep so in 300 feet you could make quite a change in direction without elbow fittings. There is usually a limit on how many degrees you can turn each joint.
There are grades of plastic sewer pipe that meet codes and require much less labor than concrete, vitrified clay, or cast iron.