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Sounds like the Oscar should be a good 'first' pinhole camera then (Though I also like the looks of the ACME series, a 4x5 OSCAR would be nice too).
Matterhackers describes their standard PLA ($27) as Opaque, (figures that the first two choices on your list are currently out of stock, and the #2 is an import from the UK).
I still have a few fractional KG cardboard spools of some 'surplus' black PLA I bought on Ebay a few years back at a super cheap price when I first built my Repstrap. The stuff passes your Opaque test object with flying colors, it's the blackest black PLA I've ever seen. I have no idea who made it or where I could buy more. (CTTOI I think there might have been a brand name on the box, if I still have the original box .... )