On prior bikes I have used the symtec system that you place 'under' your stock grips. They have always worked fine and only cost about $40.
Cold weather is coming and mama bought me some heated grips for my birthday. They are the oxford sport grips and were only $49.95 shipped from revzilla. For only $50 bucks...a very nice setup. Much cleaner install than the symtec and a nice controller with mounting bracket is included.
If you are considering heated grips...check them out!