Die Frage, ob die Verzauberung eines Gegenstands aus Kalteisen einmalig oder mehrmals +2000gm kostet, wurde ziemlich oft diskutiert, wie eine Google-Recherche zeigt.
Es gibt allerdings eine "offizielle" Antwort hierzu aus dem alten D&D 3.5 FAQ Archiv:
I’m unclear about the exact cost of adding enhancements to
a cold iron weapon. Page 284 in the DMG says any magical
enhancements to a cold iron item cost an additional 2,000
gp. I am unclear as to whether this is a one-time cost or if it
applies to each enhancement. For example, would a +1 cold
iron frost longsword cost the same as a +2 cold iron
longsword (10,330 gp) since both are “+2” weapons, or
would it cost 12,330 gp (2,000 extra for the +1 enhancement,
and 2,000 extra for the frost enhancement)? Also, is the
extra cost (whatever it might be) added to the magic item’s
base (so that it takes longer to make a cold iron item), or
just to the total price?
You pay +2,000 gp each time you enhance the item, not for
each magical property. When you first create the item, you add
+2,000 gp on top of the cost of all other enhancements you add
to the weapon, and that 2,000 gp increases only the item’s
market price. So your example +1 cold iron frost longsword
would have a market price of 10,330 gp
(30+300+8,000+2,000). The cost to create the sword would be
6,330 gp (30+300+4,000+2,000) and 320 XP (1/25th of the
8,000 gp cost for the enhancements). The sword would take 8
days to make (the 8,000 gp divided by 1,000).
If you later went back and added another +1 enhancement,
you’d have to pay the extra 2,000 gp again.
Es ist also tatsächlich "offiziell" so, dass bei jeder neuen Verzauberung +2000gm anfallen. Das wurde aber wie gesagt in Foren wohl so kontrovers diskutiert, dass eine Rivin-Hausregel wie Laf es sagt sicher nicht verkehrt ist.
