Selling Bike in Santiago
This is not easy. It is virtually impossible to reregister the bike in Chile, so that rules out locals unless you sell on the black market (stolen vehicles). Not only does this mean you would get a bad price it would also bring you into contact with bad people.
A long shot is to sell to another traveller but this complicates their lives travelling with a bike not registered in their name.
I would say a 2004 gs 1150 is worth shipping or air freighting back up.
However, I have to say this bike is going for about 8.000.000 pesos here on the used market, or almost $15,000 USD
What would you want for it?