Another "How Would You Price This?" Thread

[Amphetryon]

Question in Title:

This Masterworked set of burnished grey and black metal Full Plate Mail has been enchanted so that, for 10 Rounds per day, which need not be consecutive, the suit radiates darkness in a 20' radius. While the suit's wearer perceives this as Darkness (http://paizo.com/pathfinderRPG/prd/spells/darkness.html#darkness), anyone else perceives the area as Deeper Darkness (http://paizo.com/pathfinderRPG/prd/spells/deeperDarkness.html) (except as pertains to radius). Activating or deactivating this ability is a Command Word function. The suit grants no special ability to the wearer to see within the radius of its darkness effect. The suit functions in every other way as non-magical, Masterworked Full Plate.

[Geddy2112]

It sounds pretty similar to Mithral full plate of speed. Both give 10 rounds of a 3rd level spell that can be turned off and on by command.
The mithral full plate of speed is 26,500
Since you are using non mithral, subtract 9k
Since it does not count as +1 armor, subtract 1k
So, 16500k

Or building up
Full plate is 1500
Masterwork is 150
Spellcasting service for a 3rd level spell-15,000
16,650

So about the same. You could always make it mithral and +1 so it would be a stand in for mithral full plate of speed