RE: ...an acceptable cathode other than silver would have to be more expensive to keep from putting substances in the water that are not helpful.
A. What's interesting with the cathode is where it provides no electrodeposition whatsoever in the process. And that a precious metal such as gold(for example) would only end-up being plated after only a few runs.
The use of a stainless cathode however, is mainly a cost alternative to silver. And can prove advantageous in terms of retaining its shape where smaller gauges are concerned. Whereas a material such as copper(for example) while proving easier to identify would ultimately end-up looking silver after a few runs also. As the cathode will always be subject to plating during processing, and that these would become indistinguishable over time regardless of the finish. With that said(and as you yourself pointed out), a scenario such as mismatching electrodes could prove disastrous. And is why I recommend that an alternative cathode material such as stainless, be a different shape and size to the anode. As this provides a means from which to differentiate between the electrodes rather than to end-up mismatching them and potentially poisoning oneself.
PS. I'll be sure to edit the parts list to reflect the actual drawing and avoid confusion in the future - thanks so much for your contributions and feedback