Are you a player or a GM? If the former, ask your GM. If the latter...
Folding Plate Armor has a cost breakdown of:
Full Plate: 1,500 gp
Masterwork: 150 gp
+1 Enhancement: 1,000 gp
Special (Instant Summons): 10,000 gp
I think it's fair to call "Folding" a special ability like Delving or Putrid (straight-cost upgrades of 10k). So future armor upgrades should go up through the typical incremental fashion prescribed in the Core Rule Book. At least that's how I'd do this at my table.
