There was a pretty good article in Forbes related to the subject. Here is an excerpt:
When Congress returns from recess next week, among the first orders of business will be completing work on the Housing Bill, which would allow the Federal Housing Administration to insure up to $300 billion of mortgages. The bill has been passed in the House and a bipartisan compromise reached in the Senate committee, but Congress has yet to settle how to pay for it.
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All these maneuvers have created a plausible storyline and a low estimated cost. But the true cost of the proposal depends on the future of the housing market. Indeed, if the housing market recovers faster than expected, the Federal Housing Administration could enjoy a considerable upside. But if foreclosures occur at a greater than expected rate, the costs to the Federal Housing Administration could skyrocket. At the same time, unexpected foreclosures would further undermine the stability of the GSEs and make it difficult for them to pay the required fees, either for FHA expansion or for an affordable housing trust fund.