If you can swing it, I'd get some cheap 18" wheels.
It's a whole lot less of a PIA to change. Not to mention the chance you take unmounting and remounting two sets of tires.
I bought Bridgestone LM25s + rims at Tire Rack two years ago (commercial just came on
) and paid around $1100. 225/50-18s. They work fantastically even in heavy snow.
Tire Rack has got Michelin X-Ice Xi2 for $167/tire right now.