Grinder, from my own DPA guns, and the few others I've seen offered for sale, I suspect you're right on the serial numbers. My 4" DPA gun is very low 400s and my 5" is in the 480s. I've not personally seen any higher serial number DPA gun, so I believe a total of around 500 might be about right.
As far as prices, I did see a used/~95% 4" DPA pistol for sale at a gun show several months ago for $850.00. I don't think it came with the factory case/pouch or paperwork.
Like a lot of other people, I usually only find out about these limited run PC pistol offerings after the run is sold out, frustrating.

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NRA Life, COTEP 640