Lymington Yacht Haven's 'bargain' depended on quantity and paying by cash as I recall, so give them a ring in the morning: 01590 677071.
Personally I found the fuel berth on the RHS above Cowes chain ferry to be cheaper - but perhaps that was 'cos I only needed a couple of pints for the heater and turned up wearing a balaclava and waving a water pistol.