A former U.S. House member can cost a firm a half million dollars a year or more. A former senator can command $1 million or more, according to headhunters and hiring managers.

This all said, not every large firm needs or even wants former members on staff. Van Scoyoc Associates, the third largest non-lawyer lobbying organization in Washington with $21.5 million in 2014 revenue, zeroes in on former senior congressional and executive-branch staffers.

“I made a decision when I set up the firm 25 years ago that I would not hire former members,” Stewart Van Scoyoc said in an email. “A lot of the work we do for our clients is very granular … and for that type of work, having the deep knowledge gained from years of staff work for a member of Congress is exceptionally powerful.“