The Masters Indoor Nationals has been in Boston for 10 of the past 12 years, so I feel qualified to respond. Most of this will apply to any masters TF championship in or out.
Several points that have inaccurately been brought up, most significantly, the Masters national championship meets both indoor and outdoor are not run by USATF (national organization in Indianapolis). They are bid for, organized, and run by a local organizing committee.
Beyond housing (usually 3 rooms x 3 nights) for several masters committee games committee members who oversee various specific aspects of the championship, no one is brought in or subsidized.
As for costs in Boston, start with renting almost all of the Reggie Lewis Center for three days with the required staff/crew necessary to handle facility needs, approaching $20,000. Add in Lynx timing system and crew, athletic trainers, and 20-40 officials per day working 6-10 hour days (we pay them a small stipend which is far less than "union wages" that officials groups around here get, plus feed them, and house a few that are dedicated/crazy enough to work the full three days). That's what's needed just to be able to run the meet and produce results.
New England masters middle/long distance runners have not supported the meet in relation to their participation in other local events. They are fortunate to have the rare opportunity to run on some of the best facilities in the country almost weekly; open and collegiate invites let them enter and compete, and many can obtain passes to practice in the same facilities - even if it's "only" at a flat 200m oval. Most parts of the country are lucky to be running indoors several times a year on any track, let alone 200 meters or banked; for example, there are, what, 2 meets on Long Island a season with incomplete schedules and on a track that doesn't allow spikes. Field events are usually worse off. That's the norm around the US and the Boston area is the exception.
The meet has run in Boston for 10 years not because I or key officials particularly want to spend the better part of meet week at the end of the season sitting in the Reggie. It's because in the past 12 years, there were only 3 contested bids to host the meet; no one else has wanted to run this event.
Despite some masters claims of masters track in general and this meet in particular being a "great" sponsor opportunity , any sponsorship here in recent years is more sympathy and personal interest than a marketing investment. The meet draws about 700 entrants with virtually no spectators beyond family and friends (sort of like most non GP level TF meets). The outdoor meet draws a few hundred more, and is often the biggest show of the season in places like Orono ME and Oshkosh WI so can get local sponsorship and deals, but masters TF is a niche event and there are plenty of more visible ways to spend money on sport in greater Boston. Some real sponsorship would take efforts of a more active organizing committee, but as with most local projects in this sport, there are more worker bee positions available than individuals interested in filling them.
And if there's a question as to our having a surplus at the end of the day, we haven't paid athletes (one individual subsidized two athletes one time). No one is salaried for the meet. There's no charity. Any funds are going back into things like subsidizing an outdoor masters meet, some youth events, a series of throwers meets that wouldn't otherwise be run. And covering the 1 1/2 man office that puts these on year round.
Steve Vaitones