I looked into the idea when I was car shopping with the intention of finding the needed pieces to change the color should I find the ideal car/deal, fortunately I found one with the dark accentssince I personally am not a fan of the white accents, which by the sounds of it you aren't either. Keep an eye on Ebay as they frequently have listings for the dark accent pieces. As for the steering wheel, I don't recall seeing that piece separate so someone else might be able to chime in, but the center stack (with buttons) usually ran about $300, the bezel around the shifter was usually around 50-75 and the DIC surround was, if I remember around 100. Although that sounds pricey, and it can be, just keep in mind that you could always sell your white accents on ebay to recoup some of the money. Unfortunately it seems white is more common to be found than the dark, so you might have to price it appropriately to sell it.
Edit to add: Make sure any center stack you look at has all the correct buttons for options you have (nav, heated seats, etc).