Hey Hugo..
my first trip out there but this is my itinerary.
I'm flying Singapore Exec economy from LAX to singapore. it is a direct flight
the nice thing of the exec economy is the larger seats, more leg room. it is more costly but worth it from what people have told me. Also, i won't have to spend any time on layovers to HK or Taiwan.
Once in singapore you fly Silk on a direct flight to Manado. That flight is only on Fri, Sat, Mon and Wed i believe. So plan your dates appropriately.
the flight gets in at about 1pm. Might be able to get an afternoon dive in definitely a nite dive. flying out, you will miss the flight stateside when you get to Singapore. So you will have most of a day to chill in Singapore.
in terms of prices, i would go to the net and check out their websites. Silk and Singapore Air have different websites even though they are the same company. Kinda stupid i know.
g'luck.