Final net cost of Fed bail-out - $20 trillion?

Denis Cooper (via email) has been doing some digging...
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I notice that Ambrose Evans-Pritchard has repeated the canard that US taxpayers profited from the last major debacle, the Savings and Loan crisis:

"The RTC was created in 1989 to absorb the bad debts from the Savings and Loans crisis. The assets of the bankrupt lenders were taken over by the state, preventing fire-sales that can drive prices even lower in a self-feeding spiral. It worked well enough. The RTC sat on the devalued assets until the bloodbath was over. In the end it made a nice profit."

I wish somebody would tell him that is definitely NOT the case that "In the end it made a nice profit" - see here, here, here, or here.

US taxpayers are still paying for that bail-out, and their children will also be paying for it until all the extra US government borrowings have been repaid with interest. The final net cost remains unclear, but it will be somewhere between $166 billion and $500 billion, depending on how much interest is added.

Initially it was estimated that the Savings and Loan bail-out would need between $30 billion and $50 billion of taxpayers' money, but in the event it turned out to be more like $400 billion - say ten times as much...

If that was repeated this time round, the $1 trillion presently being talked about would eventually turn out to be $10 trillion, and the taxpayer would lose twice as much once all the "toxic assets" had been bought, and gradually sold off at less than the purchase cost, and then the necessary US government debt had all been paid off with interest - ie, the final net cost to US taxpayers could be as much $20 trillion spread over the next 30 or 40 years.

That may seem impossibly high, but the US GDP was $13 trillion in 2006, so an average of $0.5 trillion a year would still be only a few per cent of GDP. To roughly scale down to the UK - taking GDP in 2006 as $1.9 trillion, that was about one seventh of the US GDP, while the UK population is about one sixth of the US population.
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That seems to stack up to me (to within a huge margin of error), unless anybody has a better guesstimate?

UPDATE: the author of the original piece has sent me a follow up email admitting that he may have been double counting, in which the full cost would be 'only' $10 trillion rather than $20 trillion.