Perhaps the price is low but I wouldn't want the things to be so expensive that they were only legendary items. Having a few around, some of them neglected, rogue or forgotten, is a great plot device.

Party wealth is probably the most variable element from one DM to the other. Some of the pricing issues may simply be that the PCs are too wealthy and likely would retire if they were role 'real people'.

405k would give them the market cost of 4 rings of 3 wishes. I just don't think they'd ever get made. It would price them far above their utility.

What I wouldn't mind would be a limit on "Eyes of the Maker". Perhaps it might require a 1st level spell slot to function. Maybe if you burn a 2nd level spell slot you might deliver a short message through the construct. Duration wouldn't be important, IMHO, but I don't think it should be free or there is too great a chance of abuse. Even from a DM's perspective I'd like the NPC with some of these to be exhausted or preoccupied if they use them.

I think its a great monster.