I've been working with REC.gov for 2 days trying to get people added to my permit. I haven't printed it, so according to the people I spoke with at the BLM office in Price, I should be able to add up to the day before I depart. According to Joe, Customer Service Rep at REC.gov, "A permit holder may hold their permit with one person and add up to a day before departure or up to the permit having been printed. At that time the permit will be labeled as 'issued' and no further changes or refunds will be allowed."
So, I just paid $381 for a 4 day permit for 15 people. Seems SUPER SPENDY to me. Also, if you include the brain damage of being shifted around REC.gov's phone support (not) for over an hour, I think they should actually call it even..
** I have a MF permit for June and Joe said that I shouldn't have any problem adding or deleting people from the passenger list up to the day prior to departure. We'll see (I'm now a confirmed skeptic)