It cost us only 9 euros a night in the marina at Calais for a 27 footer! I don't know what their annual charges are but at that rate I started thinking about it too.
Why think of France. There are lots of clubs away from the Hamble where you can get a berth very cheaply and join in the community spirit that marinas lack. For example, river moorings in my own club are free
<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.
You don't say where you are. Try this website: http://www.plaisance-opale.com. I know people who have shifted to Calais and Boulogne this year and they're very happy with it.
How about something dramatically different like 20 houras in a jet away from home. There are advantages like 80pound PA licence fee for a swing mooring costing about 400 pound to buy. No tides to speak of, totally predictable sunny weather Oct to May and an over valued English pound to a very undwer valued Oz dollar. Warm clear water and a weed on hull growth rate that is incredibly fast.
From the costs you guys pay and the conditions you get I reckon keeping a boat in oz could be cost effective but the best part is to avoid those UK winters. regards will