Kevin, I don't know much about how caucuses are run, other than the State party sets the rules and runs them, and the rules vary by State.    A caucus might be less expensive than another primary, but still requires a lot labor, paper, and supplies. In most States, some one is going to have check caucus voters against lists of those eligible and/or registered to vote. Florida has 4.7 million registered Democrats. Although most of them would not be able to turn out for a caucus, you are still talking about needing space, organizers, watchdogs for a very large number of people scattered at numerous sites throughout the state.   Just publicizing the dates and locations for caucusing, finding and reserving space for them, announcing the rules, etc., is going to cost money. Then there has to be a count. It takes paid staff to do that much work. There has to be some sort of authentication process regarding eligibility to participate. That would probably mean employees of local government election boards have to be involved and paid.

One idea Florida is batting around is a mail-in election. The cost estimate for mailing paper ballets to those 4.7 million registered Democrats and then counting runs somewhere between 4 and 6 million dollars, according to the LA Times. I can think of no good reason why either taxpayers or the national Democratic party should pay those costs.