Having read that, it's worth noting that many of the initial technologies have been scaled back to more realistic levels.
1. IIRC they won't be using magnetic levitation. Instead they'll use air cushions.
2. It will be only a partial vacuum, not a complete one that would be difficult to maintain. To reduce air resistance, the cars will have vacuums at the front to draw in air and use as part of the air cushion system which can also be propelled at a backward angle to assist in propulsion.
3. Most of those high estimates are because they're tunneling. The hyperloop hopes to avoid this by using above-ground tubes. As for right of way costs, they also plan to utilize existing rights of way by running most of the tubes above and along the Interstates (which ALREADY have state rights of way).
I'm not saying it will or won't happen. I'm actually neutral on the Hyperloop; it's ambitious, yes, but since the scaling down of expectations things are looking more possible then it once was.