If you were offered 645USD and are non-australian then that is an average rate for a P/T. I’m sure you could get it up to 700.
TMT are great to work for (always pay on time, nice crew) and the Nomads are a pice of piss to fly and fix. Most likely a Drill Support job.
Sakhalin itself is fairly dangerous but as long as you follow the golden rules already stated, you can’t go wrong.