Like CELarson, I ride year long in the Seattle area. Temperatures will get down into the 20's, and are often in the 30's when commuting. Handlebar muffs were one of the major factors in making that comfortable for a 74 mile round-trip commute that was about an hour each way.
I first tried installing hand guards. They didn't work worth beans. The cold air and rain just went over and around to chill the hands. I found some Duck's Unlimited snowmobile muffs for $25. If you look for ATV or snowmobile muffs, you'll save a lot of money since they don't say they are for "motorcycles".

But the handlebars and controls are the same.
The way to get the muffs to work well, is to seal any gaps where air can get through. I installed them on a Suzuki Burgman that had a plastic cover over the handlebars. Air would come through in the center and run out to the handlebar ends. What I did was to stuff rags into those gaps and then I used duct tape to seal off the outside openings. Your bike will be different, but the principle applies. Stop air from running through the openings and create a warm dry environment for your hands.
An issue you may find with the muffs you buy, is making the opening ...well, open. Muffs are usually made of some kind of textile material. Mine were a little floppy and so the opening wasn't easy to get your hands inside when riding. Also, the windflow on the outside would push the muffs against the clutch and brake levers. The solution for me, was to MacGyver an "L" shaped bracket that attached at the handlebar weight screw and went forward of the clutch and brake levers. It wasn't pretty, but you couldn't see it because the muffs covered it. The important thing was that it worked.
Chris