www.oscarcontrols.com sells the controllers (very high quality and well made) for about $71, but you have to provide your own wheel and panel and (I think) hook through a mouse or opti-pac.
www.happcontrols.com sells everything except the panel, but if you need to ask about price, you don't need to go there.
What I did and highly recommend is: go to
http://listings.ebay.com/aw/listings/list/all/category13715/index.html and search for wheel or steering.
I bought an Indy Heat steering assembly for $13, including shipping.
Then gut a USB (or PS/2 or Serial) mouse, trash the arcade pc board and mount the mouse optical board so it lines up with the arcade encoder wheel.
By flipping the mounting plate upside-down and eliminating one bracket assembly, I was even able to use the original housing for a desktop controller, without having to make a wood enclosure for it.