Can't help with the value thing, I guess it's more up to what someone is willing to pay.
As for doing the FCG like a regular AK, Dinzag is way over priced, just buy a G2 set. If you don't want the BHO thing it just drops in. If you do want it you have to remove some metal from the right side of the hammer where the pin goes through, you can compare it to the stock hammer to get an idea how much needs to be remove.
For the pistol grip, the hole is there for the T nut, just remove the plate.
You could save the original trigger guard, here's a generic way of doing it. Wedge the front into the mag release and rivet or use a screw & nut at the rear.