What if I have different per diems for one event?

There are two options. Your first option is to average the per diem rates and use this amount as your event per diem. For instance: 5 days of cruise per diem and 3 days of international per diem would average to [(5 x $60) + (3 x $90)] / 8 = $71.25.

Your second option is to create two positions - One position for the cruise per diem , the other position for the international portion using the international per diem.