Electric gloves plugged into a 12 volt circuit are the best approach to warm hands, followed closely by something like the Hippo Hands handlebar enclosure. Either product will set you back well over $100, though. Another solution for occasional cold weather riding is to buy some small chemical heaters, usually sold in hardware or sporting gear stores for a couple of bucks and place them in your gloves on top of the back of your hands. They will keep your hands warm for a few hours.
But the cheap way to go for non-electric gloves is to buy a pair of snowmobile gloves. I'll bet it is getting near the time for the winter gear close-out sales. Also, snowmobile suits make great cold weather riding clothing. Snowmobile clothing tends to be a lot cheaper than motorcycle or skiing gear. If you are concerned about not having armor in the suits, you can buy a suit of armor (vented shirt and pants like used by motocross riders) that fits under your outer clothing. Since the suits are designed for wearing over your street clothing, they do well for commuting to work or school. I was able to buy a snowmobile suit from The Sportsman Guide catalog for only $60. They have quite a bit of snowmobile and motorcycle gear this time of year for under $100, but it is not the greatest quality, of course.