Bob,

I don't think U-Haul's tow dollies have surge brakes.

If you're looking for a used one, there's one here .

Have you considered that it might be safer and/or cheaper to simply drive both cars to OK? Alternatively, if you don't want to drive it, you could have the car shipped. It would cost more than renting a dolly, but certainly less than buying, then storing it for this (possibly) one-time use! Plus, you save the wear and tear on your X!