Also, budget for things like lights (you want nice, bright ones - not the cheapest you can find) and other things - a good pump with a gauge to commute with, spare tubes, eventual chain and cassette replacement, eventual cable replacement, saddle bag for tools, tools to commute with, maybe rack/panniers. Definitely fenders because you will get caught in the rain.

Also, plan on what you'll wear while commuting.

Yeah, you can spend some real money. But compare that to how much you're NOT spending on gas, and how much longer you'll be able to put off replacing your car(s).

You'll need to be prepared to fix flats and broke chains while commuting. You might want to be prepared to fix broken spokes.

And finally - just do it. It isn't hard. It's just different from what you're used to, and what you and probably most everyone else you know has always done. BFD.