The ISS's cost was substantially due to the cost of the Shuttle program. Building an equivalent space station today using the rockets and systems we have available now would likely be considerably cheaper, by a factor of 10 or more.
It should almost go without saying. The Shuttle was one of the most expensive launch vehicles in history.
There are several helpful counterpoints to hand though. Two being the history Russian and Chinese space stations. All of them, including the Russian components of the ISS, have been vastly less expensive per module than the US components of ISS. Even if you factor in building and launching modules by US standards on US rockets it's still vastly less expensive than using the Shuttle.
Moreover, we've already seen that it's possible for US companies to deliver spacecraft to the ISS in the commercial cargo program. It would actually be just as easy to deliver components to the station using similar systems for about the same cost as a cargo launch today (around $150 mil at the high end). Over the roughly 2 dozen assembly flights for the Shuttle assembled side of the ISS that works out to an equivalent cost of about $4 billion, plus extra module construction costs. Keeping in mind that such flights have already been used or are being planned to use for adding modules to the ISS (such as BEAM and IDA).
Note that the incremental cost of a shuttle mission was $450 million, but that ignores the high fixed costs. Excluding sunk development costs the average price of a shuttle mission throughout the life of the program was a whopping $1.2 billion.
OK, so that's a factor of 2.7, but not even halfway to a factor of 10.
Sorry to be a stickler on this, but I like to use the ISS as an example of outrageously inefficient science, and so I'd like to make sure this isn't completely attributable to the cost of the shuttle (which, I think we agree, was it's own terrible boondoggle).
