Countrymouse,
I have a little experience in the rental market of DC because my son did 2 internships there while in college. There was, at that time a few years ago, a large number of rentals where one person gets a lease on a 2 or 3 bedroom, and then rents out the other bedrooms to full time tenants, or interns coming in just for a semester, or for the summer.
Summer interns have a really hard time finding affordable places to live. For us, affordable meant in the 1000.00 range per month, which we were happy to pay for the 2nd bedroom in a tiny condo, sharing kitchen and bath with the married couple leaseholders.
While the market may have changed some with the current shenanigans going on there, it still sounds like the housing market is hot. Perhaps your son could take a nice 2 or 3 bedroom, and then rent out the other rooms. It might even be nice for him to have tenants as company, and he could be very selective about who he rents to. He could make enough to make his rent contribution very affordable if the apartment is in a good location.
Just a suggestion! Obviously things might have changed quite a bit since then, but perhaps something to look into.