Nitrous is the cheapest way to get horsepower quick. The stock crank and rods on the Bandit will handle around 220 HP, but it will take a toll on the engine.
I don't know how skilled you are at mortorcycle dragracing, but the more power you have, the harder it is to ride.
APE, Pingel and Schnitz Racing, all have nitrous kits that will work on the Bandit.
What ever you do, don't try using nitrous in 1st and 2ng gear, you will find yourself looking up at the stars prety quick.
Good Luck