Any bike at all will work and yes it is imperative that you spend $4000 on a titanium road bike to be able to go to work. (insert whatever grabs your fancy in place of the titanium road bike)
Well hey, with the OTHER forms of wheeled commuting vehicles out there, $4,000 doesn't even get you in the front door.
Lately I've been heavily into reenacting, for the price of my flintlock smoothbore alone I coulda had a Surly LHT, and I have a cheap one.
Mike