I'd have to say that everyone that has been here since the bike was introduced in '07... has never seen/heard of yet, a blown head gasket...
I strongly question a dealership that without pulling the head, says it is actually blown.
Lots of other things, loss of compression only is not a blown head gasket.. could be a needed valve adjustment, or some other issue.. that said, yeah, I'd figure about $1600 for a gasket replace, but if they start tossing out a $7k rebuild figure, RUN and get that bike out of there now.. crooks... don't let them rip you off..