I'm not quite sure I agree with HiYoSilver's math and list of things you need, but a great point is made:
Think of this not as a toy, or sport vehicle, but rather as a transportation vehicle.
I'd skimp on the accessories and use that money towards a better bike (your selection is kind of limited if you only want to spend about $500...seems like most decent commuter bikes start around $500). You can always invest in some nice shoes, good rain jacket, cyclo-computer and such later on (especially when they are on sale). To start you just need a good bike and a few accessories: probably a pair of shorts and jersey, helmet, and a blinky (which you can probably get in total for about 100 bucks).