The short answer: a whole lot more than it used to be. Kate Berry over at American Banker reports that Fannie Mae has recently hiked its guarantee fee to 30 basis points, the highest level in at least a decade and the latest way lenders — even prime lenders — are seeing their own margins erode. Some analysis:

Tom Lund, executive vice president of Fannie’s single-family mortgage business, said on a conference call Friday that the increase amounted to “a pretty significant pricing change,” and that despite higher delinquencies, Fannie still has “a lot of credit enhancements” on loans that were originated this year and last and have high loan-to-value ratios … David Hochstim, an analyst at Bear Stearns & Co., said Fannie is clearly demonstrating that it has pricing power, because “price increases typically don’t stick if customers don’t pay.” Fannie said last week that it guaranteed 41.2% of new mortgage-backed bond issues last quarter, against 23.3% a year earlier … Terry Wakefield, the chief executive of Wakefield Co., a Grafton, Wis., mortgage consultancy, said Fannie’s 30-basis-point average guarantee fee is “the highest I’ve seen in 10 years.”

Paid subscribers can read the rest of the story; a subscription is heartily recommended. As for the other GSE, Freddie’s guarantee fee was around 17.5 basis points in Q2 — something tells me that fee will have jumped when Freddie reports earnings next week, although the American Banker article cites spokesperson Brad German as saying Freddie’s guarantee fee has not increased. Either way, two things are pretty clear: one, the value the market is placing on a GSE guarantee is soaring; two, the GSEs are hiking fees not only in response to market demand but also to help offset what in all likelihood will be a period of increased losses on any loans they guarantee.