An interesting article from 4 years ago:
The Life of a Referee - NYTimes.com
I would guess that men's officials are paid approx. twice as much as women's.
As to training, I officiate women's small college VB. It is my understanding that volleyball was the last sport to have the official's training co-opted by the NCAA (a few years ago). The reason they were last is that there was/is an organization (PAVO) that did an exemplary job of communicating with and training officials, and the NCAA was content to let them do it until a few years ago. Now - all of the training is a coordinated effort between the NCAA and PAVO.
For VB, there are regional training clinics that, I'm sure, are required for D1 officials to attend. Each conference has an assignor, and most officials work for multiple conferences. There IS competition for sought after officials. I just work D3 and NAIA, and I started accepting assignments for this fall in January.
The NCAA and PAVO also jointly disseminate information, including rules interpretation letters and videos during the season, through a website called ArbiterSports. I currently have 8 separate ID's on Arbiter for different conferences and the NCAA. Many, if not most, conference assignors also use Arbiter to schedule officials. I receive notice from Arbiter that I have new assignments, and I have about 7 days to accept or decline the assignment.
Not sure how analogous this is to BB, but I suspect the processes are essentially similar. Hope this information has been helpful/interesting to some.