You're going to need fenders, tdawg! I never commute without them because they keep me less muddy and save an drivetrain wear. Here in the PNW they are really, really a good idea.

You can get a Kona Smoke for like, less than $350? That bikes aready comes with fenders and for a 4 mile commute it would be perfect. Spend the extra money on raingear and a top-end rack.