The largest personal expense are the flights to Saipan (airport code SPN). They seem to average $2000 round trip (US to Saipan). You might consider “split tickets” but you run the risk of flight delays or lost luggage. That’s on you – I’m not a travel agent and won’t accept responsibility/liability.
The majority of Saipan’s tourists are Chinese, Koreans and Japanese. You might investigate cheap flights through these ports. For example, in 2018 GaryR got flights to Saipan via Hong Kong for $1000 using HK Express.
You might consider flying through Guam (airport code GUM), especially if you want to climb Mount Lamlam (highpoint). Unfortunately, there is only one flight a day between Guam and Saipan on United Airlines – $249 (1st bag free).
Hong Kong/HKG
HK Express – HKG to SPN R/T is ~$250 + $94 1st bag
+ (Chicago to Hong Kong for $850-$1050)
Seoul-Incheon/ICN
Jeju Air – ICN to SPN R/T is ~$300 (1st bag free)
T’Way Airlines – ICN to SPN R/T is ~$330 + (1st and 2nd bag free)
+ (Chicago to Seoul for $1500)
Beijing and Manila
You might save a couple of hundred dollars – especially if you find seasonal specials from US mainland.