Just been doing an informal survey of G650 day rates. I have heard that one can expect $2000 to $3500 per day. The 'standard' appears to be $2500 in the US.
In Asia, my company pays one rate for contractors regardless of type - 450/550/650. It works out to about $2000 per day.
Travel days appear to be an industry issue with some clients refusing to pay for the travel day or only paying half of the daily rate.
The latest sim prices quoted for the G650 are 54k for a single recurrent and about 74k for the Full Service contract which will give you an additional recurrent on another type to maintain two types.