well, the two mentioned kits, VP and Cromwell, are the two conversions I know of. The Cromwell kit is the better detailed and probably the better to put on a kit. I know the Verlinden one will not comfortably fit the Tamiya kit. However, it is ok on the trumpeter kit and nice onthe old Esci kit, so it depends on what you have to work with. The Cromwell one was designed for the Tamiya kit.
I think Blast is coming out with a kit too...?
If you are not too worried about fit problems, I believe the VP kit is about half of the Cromwell one.