A vx'd clone is a V2 with vx parts. If you were to get a v2 and put vx parts in it like the gold bolt and vx drive then it would become a vx'd clone as they say. It would never be a true vx.
That being said you can save some money getting a vx'd clone over a true vx. But I would make sure you have the updated VX parts in whatever clone you decide to go with... They are well worth it IMO.
There are a few threads with images and more detailed breakdowns in the Macdev subforum so try to find one of those as it has all the information in it already. ROCKNROLLA got it though, the v2 has a few differences, most noticeably the bolt system. Others include the reg, feedneck arm, back cap, and colors. I have seen on several occasions people offering their v2 as a vx'd only to be discovered once the buyer receives it so ask for pics of the bolt assembly. Its not always intended deceit but it happens.
Gold bolt is 50.
VX drive train is 100 ( and it comes with the green VX detent )
If you are going to buy a VX'd make sure that they send you pictures showing/proving that it has the parts. ( Detents, Silver drive train, gold bolt )
Alot of people are selling V2's with either none, or just one of said upgrades yet still claiming to be a VX'd. If you are unsure, post the pictures in here and someone will tell you if it is a proper VX'd.
You can get them off Macdevs site.
I don't really care whether I win or lose nor do I put much stock in how many people I get out, I just like to shoot at people.
Like everyone already said make sure to get pics of the drivetrain from the seller.
The mods that are the most worthwhile on a V2 (in my opinion) are the gold bolt and the VX detents.
If you already have a gold bolted V2, then just adding the VX drive to it really is not going to be earth shattering. Since you haven't bought yet I would look for a Clone that does have the VX drive since at this point the cost of them are very close to the same thing. If you end up purchasing a V2 I really don't think the VX drive is worth $100 on top of the money you are already spending.
The VX reg is nice but the V2's works just fine and it's unlikely you'll see any performance differences. The back cap is just cosmetic.