Yeah. Some of it is quite subjective. The gap between 'This needs to cost something.' and 'This is just cool flavour that can be a freebie.' can get thin in places. I usually ask myself if there is a place in the game where the thing could actually be important enough to disadvantage the player for not having it (the iGjallar not having signal, for example). If so then it costs a point. If not then leave it free.

As for the rest, yeah, basically all you can do is compare it to other similar things and give it your best ballpark guess as to how much to charge. It's the same with flaws....