Their reference electrode sells for $125 plus shipping. The electrode comes with a 25' cable and banana plug end for plugging into a DVM. The description says:
"The user's guide is written and maintained by ABYC-certified corrosion experts, and includes test methods and reference tables that help you assess, diagnose and troubleshoot corrosion problems on your boat, yacht or dock." ---- that sounds pretty useful.

I haven't found a local source in Seattle in tonight's online search. I may order one from boatzincs.com to satisfy my curiosity and also track my experiments. I got tempted to buy one a few years ago and I recall the cost was in the $250 range. I didn't bite.