It would really depend on the final configuration and what pistol it will be used with.
Standard plastic grips won't fit without alteration (removal of material). Wooden grips made by other custom makers would need alteration as well. The alteration to the grip panels isn't rocket science but would have to be done to accept the actual frame & adapter for the metal stock. So if someone wanted to purchase an altered grip frame with the adapter fitted to it's base, the folding metal stock, and custom fitted laminated grip panels with a matching forestock the price would likely be in the $225 to $250 range. If someone wanted to make their own grip panels and forestock the price would be less.
Altering the grip frame consists of drilling a small precisely located hole into it's base and cutting a shallow but accurately positioned groove into the back of the frame.
To fit factory grip panels one would need to shorten their length and cut a precise notch into the left panel's base.
Here are some more pics: