I picked up an old home made one on Craigslist for $75. The wheel pockets are fixed and the ramps stow on the tongue. The downside is you have to leave the towed vehicle steering wheel unlocked so the unit can turn. I have the materials to add a turntable, but it still works fine as is.
I used to transfer cars occasionally for a friend with a dealership. He had both turntable and tie-rod style dollies. After using both (mostly hwy) I didn't see the advantage of the tie-rods...especially considering it was just more stuff to wear out.