Question : Have you considered flying out of an airport besides Haneda Airport (HND)?
Answer : Departing from Haneda Airport is not the only way to get to Saipan International Airport. Try looking for flights from Narita International Airport (NRT) as well. Over the next two months, flights from NRT to SPN are being booked 45% cheaper than flights from HND to SPN. Being only 37 miles away, it's easily accessible for most.
Question : How many days should you spend in Saipan?
Answer : Travelers from HND to SPN stay 14 days on average.