I don't see any
sold D140's on eBay right now for comparison, and
that's the number that matters. The "carrying case" is the problem, I think. Loose D140's can be packaged for shipping much more efficiently than in a 40 x 24 x 15 heavy, plywood box.
Shipping a 200S cab is a bear; an
expensive bear. It can seriously limit the geographic market that it's fiscally practical to ship to, and since it's a specialized item with a somewhat limited appeal
anyway, the end result seems to be is that this combination conspires to keep the overall prices on 200S cabs repressed. Unless you can find a local buyer you may well get more money for the D140's individually than you can get for the pair in the 200S cab, particularly if they are 8 ohm D140's.
In all honesty, the
most I've ever paid for a nice D140 loaded 200S cab is $300, albeit it was a 3 hr drive each way to pick it up. The last 200S cab I bought was $100,
with an old school chipboard road case but
without the D140's. Not necessarily relevent to the current market of course; the $300 one was in 2005 and the $100 one was in August 2009.
Of course a D140 200S cab paired
with its 200S head is another thing altogether; It's been some years but I've seen them bring north of $2K as a
matched set which is probably about 2 times what they traditionally bring if sold separately.