Even with the extra tooling costs it will cost much less than electroless nickel plating. Coverage is guaranteed and you can avoid plating costs entirely. Galvanneal and electrogalvanized sheet stock work well in many cases for computer frames and chassis. Many computer manufacturers are now using precoated steels for some or all of their sheet metal parts. Pop the top on your PC and have a look inside.
Chances are it's precoated steel inside.
In a benign office atmosphere, precoated steels can provide adequate corrosion protection, even on cut edges. It may not work for everyone, but it's well worth considering. From a practical point, I would find a plater that would do one for you in Alkaline zinc with a yellow chromate. Any contract based on the demo part should have very specific thickness in the corners specified. Quality zinc is the way to go.