“Much of the discussion of the cost of the bailouts is getting it wrong,” David Colander, an economist at Middlebury College, says. “What matters is what price they buy the assets for and the price they sell them for. That’s where the real action is.”

Figuring out how much to pay for the assets is the first problem. The drop in house prices and rise in foreclosures have made it clear that these securities are worth considerably less than banks expected. But there is enormous uncertainty about how much less.

Based on the underlying fundamentals (like the current foreclosure rate and the one forecast for the future), many of the securities appear to be worth something on the order of 75 percent of their original value. But thanks to the fear now gripping the market  not necessarily an irrational fear, given that most forecasts have proven far too sunny over the last year  very, very few of those securities are trading hands. Among those that have, the sales price has been roughly 25 percent of the value.

Which price is the government going to pay? As Mr. Colander puts it, that’s where the action is.

It clearly shouldn’t pay 75 cents on the dollar, or anything close to it. That would mean the Treasury Department  which, in the end, is really you and me  was assuming nearly all the risk. But it probably can’t pay 25 cents. That might fail to fix the credit markets, because it would do relatively little to improve financial firms’ balance sheets. Firms might then remain unwilling to lend money to businesses and households, which is the whole problem the bailout is meant to solve.

The most obvious solution is to pay more than 25 cents on the dollar and then demand something in return for the premium  namely, a stake in any firm that participates in the bailout. Congressional Democrats have been pushing for such a provision this week, and it’s one of the most important things they have done.

The government would then be accomplishing three things at once. First, it would take possession of the bad assets now causing a panic on Wall Street. Second, it would inject cash into the financial system and help shore up firms’ balance sheets (which some economists think is actually a bigger problem than the bad assets). And, third, it would go a long way toward minimizing the ultimate cost to taxpayers.

Why? The more that the government overpays for the assets, the larger the subsidy it’s providing to Wall Street  and the more it is pushing up the share prices of Wall Street firms. As Senator Jack Reed, Democrat of Rhode Island, notes, the equity stakes allow the government to recapture some of the subsidy down the road. It’s a self-correcting mechanism.