You are into serious distance over water with 200 nm. You will need a twin with floats, a liferaft, probably immersion suits for passengers etc.
Also your destination will need fuel as you are unlikely to have a helicopter with 4 hours transit fuel + task fuel + reserves.
You will need to discuss the whole task in a very detailed way to an operator as this will be quite complicated. I would recommend speaking to PDG in Inverness as they will be able to give you a ballpark figure for you to start budgeting on. This will not be cheap though.