OK, so I settled on the PT-10 from Pac-Tec.  I chose this case because:

• It is still in production and in the electronics suppliers (at least in the US where I reside.)
• all of the panels can be defined in 2d cad drawings, which i can later send to production in any material I like, for instance transparent or black plexiglass / acrylic
• The cost for the case without panels is approximately 19 dollars US (before shipping, which in the continental us is about 10 dollars).
• the non-production kit with all of the panels installed as blanks (for making the prototype) comes in at approximately 44 dollars + 10 dollars shipping before VAT which is about 2 more dollars.(yikes!)
• The hope is to get the cost of the case, and pre-cut inserts down to around 50 dollars -- so if you can get the PCB / panels shipped at the same time the total cost for the case with the keyboard should be well under 100, this is pending the cost of fabrication for these things which I am still new at; and have no idea what all the costs are, but the lions share of the price is in the shipping.

For switches I piked these interestingly colored knock offs found off amazon:

These have the plastic PCB mount stand offs, a set of 45 was 18 dollars on amazon.  This is by far the cheapest switch on amazon -- you could most likely source cheaper from the electronics supplier and I am still not 100% sold on through hole switches -  I still think I can find a surface mount switch for considerably less. but doing the routing on a single layer, PCB without some way of managing crossing tracks is difficult.  Consider also the initial membrane was two layers to begin with.

For the key caps i settled on a simple PBA retro looking switches:

The key caps have a XDA profile so the key height does not change from one row to the next.  This is super important because we are moving some of the keys from their rows and we want it all to line up properly.  So later on, builders who care about this detail will need source keys with the same profile.  Its a standard so I am certain there are keyboards out there with this particular profile.

I am still on the fence for my ZX81 build as to weather or not to use a full picoATX power supply (which would have all the niceties like over-volt protection, reverse current protection as well as a real 3.3v rail for mods.   Later on when I do the terminal build I will definitely go for this, as it makes the case considerably more useful for a larger range of single board computers.

Now it's just sit back and wait for all the parts to come in.   Most of the small bits are here as of today.  The case will be here mid week, and I also ordered a sticker set for the key caps to put over top for the ZX81 build.  hopefully soon as I am chomping at the bit to get the wheels turning on this project!