There are some really good cruise deals on repositioning cruises – ones where you fly out to the Med or thre Caribbean and cruise back to Southampton or vice versa.
However this can be complicated as your car is often parked at the embarkation point, generally the airport and you are dropped off at the port many miles away. Some cruiselines do provide a return coach if you book the cruise in advance however on the late deals you are often left to your own devices.
National Express offer a daily departure from Southampton to Gatwick from £27.40pp or Southampton to Manchester Airport for £36.30pp. They can all be viewed and booked via http://www.nationalexpress.com/
Alternatively you can take the train from Southampton Central to London Gatwick for £14.90pp or to Manchester Airport for £23.50pp. These can be booked http://www.thetrainline.com/. Remember that train tickets are cheaper the more in advance that you book them.