how would I simply toggle a shader on or off? Are their any precoded shaders that I could add to make an object semi-transparent?
Not sure what you mean by on/off. You can enable/disable the renderer, and it won't render. Or the entire object. Or you can replace the material with another one.
Most shaders have a Main Color, and that main color includes and alpha channel, so put that at like halfway. You can also use textures with alpha channels, I like PNG myself.
I'm not sure I fully understand what you mean toggle shader. You can't just turn a shader off because that tells Unity how to render the object.