For best mileage: The Honda has it. Between the 3 bikes, the honda is the only one with a single piston engine.
The Honda gets about 80mpg. (most because of it's single piston engine)
The Hyosung gets about 70mpg. (V-twin engine, but lower revving then the Ninja.)
The Kawasaki gets...
Give me the directions to your local dealership and I'll buy it for myself if you're not interested.
That seems fairly reasonable. It's barely past the break-in period and the model is a 2010.
But if you want to get a better price, remind them that they're selling a damaged motorbike...