Bare in mind it is tax free and also paid when you dont do overnights aswell so a day trip can be worth $20-$45 dependant on the hours worked on top of your overnight allowances.
It really can add up nicely and on paper your fortnight salary will be similar to that of someone who is earning 50k as a large chunk of your salary is tax free.
Overnight spending can vary, I find if I have an away pattern of all early starts I spend less as im not out drinking and I really only need dinner after getting in that afternoon and breakfast is usually available onboard.
I dont work for Pac Blue, but a similar company with similar patterns and pay structure.