While I don't think it's what the reporter meant either, at least one bridge has been stolen before. http://old.post-gazette.com/pg/11280/1180364-455.stm#ixzz1a9...
I can't find the weight of that bridge directly, nor how they arrived at the value estimate, but if I'm reading it correctly, this (http://www.steelonthenet.com/commodity_prices.html) seems to say steel scrap was going for $428/ton in October 2011, so from the "estimated $100000" we can guess that it was about 234 tons of steel.