This is what the website says -
"Gold members receive $45 per person.
Platinum members receive $80 per person.
Diamond members receive $135 per person.
The above amounts are in US dollars, which is the currency used on board all our ships.
Visit our Cunard World Club page to find out more about these and other benefits.
Please note, My Cunard cannot accept internet bookings using internet credits, so Cunard World Club members with credits will have to wait until they are on board before booking an internet plan. The same prices quoted on My Cunard will be valid on the ship."