How lucrative is academia?

Apparently, very.
From WSJ's Real Time Economics:
The Federal Reserve announced today that governor Frederic Mishkin plans to step down at the end of August and return to academia. ... Meanwhile, Mr. Mishkin may be giving up a say in monetary policy, but his return to the academic world will surely be more lucrative. His financial disclosure report, released in 2007, shows that in the year before joining the Fed in 2006, he made a tidy sum dispensing advice to central banks, governments and business groups around the world. He collected a $134,858 consulting fee from the Icelandic Chamber of Commerce; $63,188 from the Riksdagen, or Swedish Parliament, who hired him to co-write a report on the Swedish central bank; $15,600 from the Central Bank of Chile, $15,575 from the Bank of Korea, $9,161 from the Bank of Spain and $4,250 from the Bank of Canada. That was all in addition to his salary from Columbia University.

From Bloomberg:
... like most recent Fed governors, Mishkin took a pay cut to join the central bank. His salary is $172,200 this year, compared with $300,000 at Columbia in 2005. Mishkin also earned $434,000 in royalties from Pearson Plc in the 18 months ending June 2007, according to a financial- disclosure filing last year. Pearson publishes Mishkin's best- selling textbook, "The Economics of Money, Banking and Financial Markets,'' now in its eighth edition.
In the same filing, Mishkin said he received a $75,000 "advance and grant'' from Pearson for a not-yet-written textbook.