Not sure how much they sell for on Atlantic, but they tend to sell for about 200-250k on Lake Austin (which in terms of population is about the opposite extreme from Atlantic).
Do note that most existing stockpiles of 120 Smith BODs probably got turned in for points during the cleaning.
Because some people are greedy bastards and don't know how to price BODs, many places (especially Luna) have vendors charging almost that much per small BOD for the set, as for the reward, which is insane. (sorta like how many of the taint-requiring items sell for the same or less than 1/10 the taint used to make them)
I personally only charge 5k or 10k per small, and for the large - after all, for the three most common larges that give a 120 PS, the filling smith is gonna have to have a MINIMUM of 2k Shadow ingots, or 1000 or 1500 Copper ingots - and that's if all items made are 100% exceptional (which would take using a hefty ash as well as a talisman).
However, that said, the smalls are pretty darn common from BOD runs, and if you can find someone with the BODs priced reasonably (no more than 30k per) you should go that route, if only because (if you aren't to your current cap yet) you can GAIN SKILL filling it, and will be getting part of the gold back in the reward. If you have most of the BODs already for a set, buying 1 or 2 to complete would still be in your best interest, as long as they cost less than 100k.