Genus Loupe Viewfinder. Under $100 US.
I recently stumbled upon this LCD viewfinder from Genus. I found a little info here on the forum and thought it was worth posting in the News section. The 2.5X viewfinder attaches via a sticky frame. It slides on the frame via a dovetail. It looks like it might be a comfortable solution for under a hundred bucks. Here is a little info from the Genus website.
The Genus Loupe Viewfinder is the ultimate tool for use with 3-inch LCD screens. With a 2.5X-magnifying lens, the G-LV allows you to clearly see your images on a larger scale. Easy to install and adjust, the Genus Loupe Viewfinder Kit comes with one black hood, one translucent hood, a mounting frame, magnifying lens and a convenient lanyard.