"Luxury" housing isn't what's being built - "expensive" housing is. Because it's "expensive", people use the word "luxury".
"Housing" isn't expensive - land is. Expensive housing is being built - in downtown Boston - because the land is expensive. Labor and supplies will cost the same whether here or outside of Boston (but probably more than in other states where workers aren't paid the same wages).
Two developments - both in the Combat Zone, both under construction - show this. Kensington is a $172 million project (I believe, construction costs only, not land) while Hong Lok is $33 million project (same). Kensington will have 385 units while Hong Luk will have 74 units. Doing the math, each comes out to a cost of about $445,000 per unit.
That's cost. If this was a condominium project, you'd have to add in a profit on each of these of, what, 20%? So, a market price of $550,000? I don't know how apartment developers calculate return on investment so I don't know what the equivalent is in rent.
The difference in the two projects is that Kensington is a "luxury" development while Hong Lok is a low-income development for seniors. Rentals at Kensington will be ... I dunno, $2,500 for a studio or one-bedroom, $4,000+ for a two-bedroom? Rents at Hong Lok average $500 per unit, possible because it was built with a mixture of public and private funds from 23 sources - including $7 million from the developer of Kensington, in fact.
A $300,000 condominium with 3% down (FHA loan) will run you $1,300 per month (before FHA lending fees, etc.) plus probably $180 per month in property taxes and $200 in condo fees, for a monthly housing expense of $1,680.
Added note: If you want to see what $500 per month gets you for an apartment, here are some photos w/ background on Hong Lok:
http://sampan.org/2013/03/hong-lok-house-expands-to-house-more-chinese-seniors/