50mm 1.8G vs D

I have a Nikon D5100 and I'm planning to buy a Nikon AF 50mm 1.8D. I know it won't autofocus with the D5100, but my hands are tied, because AF-S 50mm 1.8G is currently unavailable where I live and it costs almost twice as much as AF-D version. My question is how difficult is it to focus manually with wide open aperture? I'll be using Live view to focus. If I choose not to use the Live view, then I'll be using the rangefinder. How accurate is the rangefinder when the lens is wide open at f/1.8 resulting in a shallow DOF? And how different is the optics quality between AF-S and AF version? Is it really worth twice as much?