Cost of commuting
Not necessarily so much. I've been commuting three years, 20 miles round trip for one year (it was shorter the first two, but I was car-free those years)
Bike: a good road bike so you're commute doesn't take too long - $129 (I normally do the 10 miles back in 32 minutes, fast enough for my purposes)
Helmet: $19
Panniers: $0 - 2 zipper fabric bags slung over rack
aero tailbox: $15 material cost
Patch kit + tube: $10
Clothes (1 set): no special clothes needed
Winter Gloves: already owned
Jacket: already owned
Headlights: $20 (LED mag light)
Blinkies : $8 (simple circuit with bright LED)
Repair/Maintanence: ~$100 (three years, including lube, tires etc).
It comes to around $100/year.