The cost of these things is calculated mainly from their antitank lethality.
Launch the cost calculator tool and you'll see that some 90% of the cost of a SPATGM is made up of the weapon cost (weapon abilities * ammo loadout). For the same quantity and same anti-armor power, a missile weapon will be much more expensive than a gun weapon mainly because of the accuracy.
Compared to a missile-firing IFV or tank, SPATGMs tend to have more missiles, themselves deadlier (compare the data of a Krisantema and a Refleks).
I don't know about SPATGM/ATGM team RF and FC rating, that was a question I was going to ask too, so if Don or Andy or any game vet are around I also would like some info on why all these never seem to get decent electronics!
I think that basically these values are mostly needed for gun shots calculation, but then again I may be dead wrong!
But consider that if you add FC, stab or RF to a SPATGM or anything it will make it costlier, even if it doesn't immprove performance.