[Freeze]

The difference between a $200 G&G and a $400 VFC is that the VFC is full metal, and boasts an excellent reputation for having one of the best bang for buck higher end guns.

The difference between a $400 VFC and a $600 VFC is likely the production date and updated internals which may include a built in MOSFET (recommended if you plan to use LiPos). I'm not entirely sure about this because I'd buy the $400 one and just overhaul the internals immediately anyways (which I did actually).

VFC is also reputable for the ability to accept basically all decent aftermarket parts with little to no modifications.

Realistically if you plan to upgrade the gun in the near future (or maybe a year later), I'd recommend the $400 VFC.
If you want to buy a cheapo starter gun to try the game and see if you want to stay, I'd recommend the $200 G&G.
I'm entirely unsure about the $600 VFC I have no experience with that.
I would also 100% stay away from Krytac, they have some proprietary bits, and are known for the lower receiver to crack at the grip area, and once that happens you might as well throw the gun out.

Also as a side note, I recently (if 2 months if "recent") purchased a VFC from Aventure Airsoft Lanaudière, they have excellent communication, definitely would recommend.