The models with Roman numerals were discontinued years ago and are old technology. I doubt if you'll find a new VX-III. If it is still new it is at least 10-15 years old. The VariX-III's are probably more than 20-30 years old. The VX-3 is a newer design. The VX-3i is the newest generation and should cost more.
In my opinion there isn't enough difference between the VX-2 and VX-3 to justify the price. I haven't used the VX-3i, but while probably better, it is even more expensive. For me If I want to spend more than $300-$350 for a VX-2 I think there are better scopes than the VX-3 or VX-3i.
About USA made. As far as I know all Leupold scopes are USA made other than glass. Many of Leupolds other products such as binoculars and range finders are now imported.
Just to clarify, the VX-I and VX-II series succeeded the Vari-X IIc in 2001. The lens coatings were upgraded in 2004, but there wasn't any change in the naming protocol to easily identify the change, so if you're going to buy a used Leupold, it is useful to know that the VX-I/VX-II scopes with serial number suffix J/K/L have the older lens coatings.
The VX-1 and VX-2 series succeeded the VX-I and VX-II in 2012.
