My first winter I got a pair of used rims on ebay for $50. Mounted a pair of Nokian 296's to those. It takes me less than 10 mins to switch rims. Since, I've bought a pair of rims (Rhyno Lites) to match the ones I have my road tires on. I got those on sale at the LBS. Machine laced, but they're still good rims. I don't like to ride the studs on dry roads too often if I can help it.
If you do decide to go that route, of buying a spare set. Just make sure the width is close to the width of the ones you already have. Less hassle with the brakes. Clinchers that is.