To those who are worried about the wiggle of a fiver sitting on a steering axle, the steering mechanism locks over 20 mph.
The one unit I looked at uses an F450 front axle with hubs, brakes, etc. for the dolly axle.
Also, you replace your hitch with their Class 5, three receiver hitch.
The unit I looked at can be found here: http://www.automatedsafetyhitch.com/
I have no idea the exact cost, as there are several options, and their website only has a few prices. I would guess you would be looking at $2,000 to $2,500 easily.