Only you really know what type of terrain your rig will see, and how aggressive you intend on being when negotiating said terrain. Both types of skid plates have their drawbacks and advantages. If it were me, and I just wanted skids for that "just in case" scenario where you tag a big branch or come down on a rock wrong, then I would take a look at the ARB skids for the 4Runner. They will certainly not last if you plan on rolling the Rubicon every weekend, but for the type of terrain that you will see in you region, and if you are careful what you drive over, then they should protect your expensive underbelly from that errant object. They are a cheaper option for sure, are already powder coated, and made to fit your rig. The downside is that they are thinner and subsequently less durable when subjected to constant abuse. Different models depending on whether you have KDSS or not.
Thanks for the tip on the ARB 1/8" steel plates. They look to be exactly what I am looking for: cheap, moderately durability, lighter. Like you pointed out, they probably aren't the preferred skid plates for repeated trips through the Rubicon, but that isn't what I am looking to do anyhow.