Costs under a grande? That's a tall order for a new, quality bike. I think I'd be more inclined to pick up a used bike and kit it out as best I could. Disks would be preferable in most winter conditions, as I recommend on VeloWeb's Winter Cycling page.

You might also want to check out the Reader's Rides page to check out how others approach year-round commuting bikes -- there's some single-speed/fixed riders there.