I question the $100 million figure for LV (though that may well be right). There are a lot of forces there who seem opposed to the monorail, so that could be an inflated figure to ensure it's doom.
Also - Vegas politics/dollars are very different from Reed Creek Improvement District politics/dollars! Still - I'm sure it's extremely expensive, but I doubt prohibitively so for all time.
While I agree with starbox about the monorail clashing with the WL theming, it's not exactly a Polynesian or Victorian accessory, either!!
The problem with the monorail is that it's fairly inflexible, and not nearly as safe as a light rail would be. It would be much cheaper to build and re-route a light rail system as needs change than it would be to extend the monorail track. As for safety - if you're stuck on the track, you're stuck on the track. I know they can find you, get you down, or tow you to a platform, but a larger system would mean far more safety systems - that might be what makes it prohibitively expensive.
Dirk