There are lots of reports of low bids for stimulus projects. (Here, here, here and here.)

This one is especially low: Fixing a roundabout in Missoula, Mont., will cost $600,000, exactly two-thirds of the original $900,000 estimate. (Thanks to Geoff Badenoch, former Missoula Redevelopment Agency head and now ProPublica Reporting Network member, for passing along this story.)

Competition and lower supply costs are the two factors used to explain lower bids. But a 30 percent difference is significant. What is the profit margin for companies like Knife River, which made the roundabout offer?