Ooops almost forgot to answer that one fer ya. This wouldn't be the sole investigation for these agents. These agents are all working a case load. This deal was probably an interuption for some agents who were brought in to assist with warrant service and without a breakdown of who did what, and salaries plus other expenses, it may have cost more than the number you quoted (or less.) They may have even included the new guy who went to Starbucks on the coffee run. It seems the Feds move their agents around a lot on details. When Kerry was on the road campaigning in our town, I was very surprised to see ICE agents on part of the security team.
I kind of suspected that. Then again, as you said, it was a big investigation, so I would also suspect more time was devoted to this, and the time spent on the other cases was probably reduced somewhat.