An actually affordable unit may be one which was constructed to appeal, marketting-wise, to someone making $100,000/year, and instead is sold for a somewhat lower profit to someone making $60,000/year, because there are fewer $100k people than there are $100k units. "luxury" and "affordable" are in quotes for a reason: the difference is language, veneer, and floor tile, which are trivial expenses relative to the location-scarcity of the land & permits. A $3,500/month rental unit in SF might sell for $70,000 in suburban Cleveland with an identical interior.