The "RADIO xxxx" (which they inherited from its earlier organizers) is a very big deal, indeed -- not sure how big the budget is; an e-mail to Bruce Phillips would probably answer that question. The cost per attendee is very modest. (and, presumably, smaller groups are readily accommodated by the hotel, presumably at lower cost).
NEARC's own, much more modest swapmeets are held at a slightly funky place* in Brookline, NH. Just a few miles from MA 111/Pepperell, MA (or a few miles from Nashua, NH on NH 130). Not exactly trivial to get to, but it's probably cheap. Not really good for multi-room setups, but plenty of space.
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* "Brookline Event Center-32 Proctor Hill Road, Brookline NH 03033" (More like an Elks' Club kinda place than an "event center", I'd opine).