Some thoughts from Stewart Money, with which I agree:
While presented as a legitimate concern, $4.5 billion is after all a large sum of money, and a very tall hurdle to overcome, it still leads to an interesting counterpoint which the authors of the NASA funded study do not address. NASA is well on the way to spending $16 billion to get the Orion capsule alone through one crewed flight, a number which excludes the development costs of the Space Launch System as well as its ground infrastructure. The agency cannot even begin to put a price tag on gong to Mars. It would be interesting to see the same team run the numbers on that.
There is no doubt that Mars One is [a] risky concept, and if it is to ever gain real traction, it will have to endure a lot more scrutiny than presented in the MIT study. It should probably begin with a clear statement that Mars One is meant as an evolving concept, in which the final product may differ considerable [sic] from what has initially been put forward on a time frame which like all space projects, is subject to change. At the same time, its many critics might want to at least consider how much of the risk to any future Mars mission, whether one way of with a return ticket, could be reduced through advancing the Technological Readiness Level (TRL) of some of the core technologies the MIT team identifies.
Finally, they might want to ask why the U.S. is committed to a very different, but perhaps even more financially implausible plan.
[Update a few minutes later]
By the way, Bas Lansdorp has responded in comments over at Marcia Smith’s place.