I don't really know but will guess it wont be cheap because the engine has to be removed first:
GL1200 Engine Removal: http://www.goldwingfacts.com/1200engineremoval.htm
GL1200 Stator Removal: http://www.goldwingfacts.com/1200statorreplacement.htm
GL1200 Engine Removal: http://www.goldwingfacts.com/1200engineremoval.htm
GL1200 Stator Removal: http://www.goldwingfacts.com/1200statorreplacement.htm