There is a few threads on this subject and I recall, everyone seems to post the cheaper ones are junk, and are hard to move by yourself.
I have two cheaper sets, one double the other in $......both require two people (or more) to get rolling.
I bought a set of high dollar GO JACKS commercial ones (cash...cheap sale) from a defunct body shop that worked great, had the jacks on them and they would lift the tire off the ground by jacking two sides together against the tire.
One needed new casters and one was need of repair but roll great! Not cheap new, but work.
Here they are and some others on this site mid way down:
http://www.etoolcart.com/automotive-wheel-dollies.aspx