Bike: Generic Road Bike assembled with love and tender "Get this POS outta my shop" by my LBS $150
Helmet: $45 but I've had it for years
Maxpedition Backpack: $40 because I got a deal
Top Tube Pack: $8
Patch kit + tube: $5 + $4
Clothes (1 set): I wear regular shorts or BDU pants that are part of my hiking gear
Gloves: $25
Headlights (3x high output LED) : $20 because my LBS loves me
Tail Light: $20
Repair/Maintenance: I turn my own wrenches

Total cost: $317

I ride the subway and ride ~6.5 Miles three days per week to get to an internship. Would an $800 bike be nicer? Sure, but it wouldn't make me particularly faster considering I tend to hit every red light with the rest of the cars in Downtown LA .

I might add a Rack and make/buy a bag so figure another $20-$60 depending on how "roll your own" I go.

Now considering a tank of gas runs me $60 and I'd be spending an extra tank of Gas every week or week and a half because of rush hour traffic each way... even having a $1000 setup will amortize out quite nicely rather quickly seeing as I'm doing it for $3/round trip ($36/month) + some sweat v.s. an additional $120+ of gas per month for a year (the length of my internship).