And if you can't find anything concrete by searching, something I posted 12 months ago here.....
The Honolulu light rail system currently being built has budgeted an average of $57.5m a mile for track. Despite being light rail not monorail, it's comparable in the fact that's it elevated to the same kind of height. But given how heavily congested significant parts of it route is, I can imagine that's significantly higher than what the cost would be at WDW without the congestion (existing buildings, road etc) and the same level of planning consent. Still, you probably wouldn't get much change from $30m a mile just in track costs.
By comparison in the last year, Bob Iger 'earned' $46.5m. The track distance between Epcot and the TTC is a little over 3 miles.
Can they afford it? Heck yes. Disney Parks & Resorts earned profit $2.66bn last year (Disney as a whole $13bn profit).
Will they do it? As many people have already stated, almost certainly not because of that cost.
Disney hasn't scraped together the dollars for a new E-ticket in over a decade now (maybe $100-150 for something very good), there's no way they are going to invest that and more connecting another park to the monorail which will have close to zero ROI.
I'd love to see them connect up all the parks and resorts, and eliminate all the buses (at least 99% anyway). Is it ever going to happen? I don' see it.