Pleanty of scooter shops on R14 with a couple opposite DSME West Gate.
Not sure of costs as don't drive one myself.
Also, with Goeje having the worst reputation for driving in the whole of Korea, you are probably better off cocooning your self in the relative safety of a car.
FYI, cars/buses/trucks/taxis all jump red lights so u have to be carefull.
Also the smaller you are on the road, the more vulnerable you are.
Unless you plan to be a delivery boy and weave through the traffic like a GP1 rider, but carrying hot food, then I would steer clear of a scooter.
Hope the above helps?.....