Well, I finally got somewhere! Here's a brief recap for future reference.
The key seems to be to set up the armor not as a regular mundane armor (on the Armor tab of the editor), but rather as a magic armor (on the Armor, magic tab) even though it is not "magic"; it facilitates the transitions required.
I had to start from a copy of the iElvenChn thing: for some reason, if I started from scratch, even adding exactly the same things (except for the armor type), the price of the base armor would not be counted in the calculations.
The following script runs flawlessly so far, at First - 10000 (if later, iPriceCash is not accounted in final price)
Code:
perform gizmo.findchild[BaseItemPw,"thingid.ipAMSAArFo?"].setfocus
doneif (state.isfocus = 0)
focus.field[iPriceCash].value *= 0.5
For a single power, you can also use
Code:
gizmo.childfound[ipAMSAArFoc].field[iPriceCash].value *= 0.5
Thank you all for your help!