Hi,
Its pretty unlikely you will get a GT-31 second hand, or even a GT-11. Those people keen enough to upgrade to the GT-31 will probably keep their GT-11 as a redundant GPS. You may be better off shopping around for a new GT-11 as there may be old stock that has to clear.
I bought my GT-11 at Wind Surf and Snow around eight months ago.
Caloundra City Sailboards have the GT11 for $150 new.
My mate drowned my GT11 and replaced it with a GT31, but honestly I would have been be happy with another GT11 
I've got a brand new GT31 I bought and have never used.
Send me a PM if you are interested.
Tony
